I am considering two bikes: the Rivendell Cheviot (60cm) and the Pashley Aurora (22"). From a (mostly) purely frame builder standpoint, I am soliciting feedback. I am curious about handling, ride, robustness, and overall design decisions made. I am reading a book about bike building but am nowhere even close to having the eye of a pro.

CHEVIOT

Aurora | Ladies Classic Bike, All-Rounder & Great City Bike | Pashley

For background info: I am 5'10", 155lbs, 35" inseam, 57 years old, and want a women's bicycle that is versatile, fun to ride, and handles well. I have owned way too many bikes from road bikes to Dutch bikes, from Trek to Jamis to Workcycles; and I appreciate different aspects of all, and look to this bike to be the balance between them.

They're both lugged steel frames, made of quality tubing. The Cheviot is made in Taiwan (at a very good shop) and the Pashley is made in Stratford-upon-Avon, UK.

The differences will be in the frame design, and the components equipped.

The Rivendell Cheviot probably has longer chainstays. That's Grant's latest favorite design feature. Supposedly, it gives the bike a cushier ride.
The Pashley is a true, traditional mixte frame, with two smaller diaga-tubes. Whereas, the Cheviot has a single diaga-tube that splits into stays at the seat post. The Cheviot design is stronger, but the split mixte stays on the Pashley are quite lovely.
Due to these differences, I'd expect the Pashley to flex a bit in the main frame, and the Cheviot to flex a bit in the stays. Of the two designs, the Cheviot is more stout but may still ride as nice.

The Cheviot has other unique design quirks. The name is funny (and spelled differently on either side), the headbadge and lugs are gorgeous (with a couple filled-in windows), it has a kickstand plate (helpful), it has a pump peg, and comes in a couple color choices.
The Cheviot also will fit wider tires than the Pashley.

The Cheviot is sold as a frame/fork, and components are all chosen separately. So, you can spec whatever components you want with any type of drivetrain.
The Pashley is sold as a complete bike, with an 8-speed Alfine Internal Gear Hub (IGH), and nice accessories like a Brooks saddle and fenders.

The Cheviot will be more expensive in the end, but you build it exactly how you want.
The Pashley is less expensive, but has a nice build on it (if you want an IGH). The price will be about the same if you decide to swap out a bunch of the Pashley parts.

Disclosure: I own two Rivendell frames, and they each have a wonderful ride. I'm obviously a fan of Rivendell, but Grant's recent direction toward stouter, upright-riding, longer frames doesn't fit my riding desires.
Though, it sounds like these new designs would work well for your desires.
I'm younger and prefer sportier drop-bar bikes, so I have a '97 Rivendell Road Standard and a '10 Roadeo.

Thank you for the reply! Comments and Questions embedded below.

I passed along a Reynolds 531 Mercian mixte I found, used, in Eugene, to an X-GF in Berkeley..

downside to using High end thin-wall tubing in the Mixte layout, was the head tube was relatively easy to torque
with the handlebars .. front wheel track could be moved sideways ..

She has an old asian made Gitane badged one ( from our Uni Time in the late 70's.)

the thicker tube wall . hi-ten steel was less noodly ..
even still in the Mixte twin thin top tube rear stay design, because they use more of It.

So IMHO the larger round top tube one would probably be better in that regard..

Then strip parts you dont like , put on those You Do..

Touring bikes have used longer chain stays (~45 cm) for ages. This gives them a longer wheelbase, which has more stable handling (and better pannier clearance). In contrast, racing bikes have short chain stays (~41 cm) for quicker handling.
Grant Petersen at Rivendell has extended these chain stays even longer to 50 cm (on the 55 cm frame, which is probably your best size). Folks that have tried these "long Rivendells" love the way they handle.

Regarding handlebars, swept back bars like Rivendell's Albatross are usually more comfortable than a flat bar because they offer more hand positions. However, some folks don't like riding with their wrists parallel to the top tube; some find the horizontal wrist position of a flat bar more comfortable.

Frame flex is caused primarily by the diameter of the tubing used. The two small-diameter mixte tubes on the Aurora will flex more easily than the single large-diameter tube on the Cheviot.
On both bikes, the diaga-tubes are firmly attached to the seat tube, so neither should flex in that area. I expect the Aurora to flex more in the front triangle (due to the skinny mixte tubes); Bob's response above describes how a similar bike (UK-made 531 mixte) would flex. I've seen bikes like that, where you can torque the fork/head tube and seat tube a couple degrees away from vertical. Front triangle flex is disconcerting.
I expect the Cheviot to flex a bit more in the rear triangle (due to the extra long chainstays), which shouldn't affect handling but may provide a little suspension/damping.

You're correct that the skinny tubes are the wrong diameter to attach any accessories. But lots of folks love how you can hold a U-lock between the mixte tubes.

It's too bad that Pashley doesn't list the exact geometry for the Aurora. It looks like you can request a brochure; maybe that would be more detailed. Hopefully they're quick to reply to your email.
The 55 cm Cheviot is made to fit a 650b x 45 mm tire, plus fenders (60 cm fits a 700 x 50 tire). Plus, the folks at Rivendell are happy to talk to you on the phone or email. If you want to talk to Grant, you probably can.

Where are you located? Rivendell has a shop in SF, and dealers in a handful of other cities.

With the Cheviot, everything is a la carte. If you want their friend Rich Lesnik to build you an Alfine 8 wheelset, they'll set that up. They'll probably try to sell you an SP dynamo front hub (which I also recommend).
Or, if you want to order your own wheelset and ship it to Riv for assembly, they'll do that too. But the 55 cm Cheviot is 650b, which is less common, so you won't find as many pre-built wheelsets.
Regarding the shifter, you can use the Nexus 8 grip shifter with the Afine 8 hub. I don't know how tricky that would be to swap out on the Aurora.

FWIW....

I just looked at a Rivendell....at my LBS (which is a dealer) and the build quality is simply beautiful.

I personally have have a lot of pain issues with flat bars and really advise people to stay away from them unless they are actually mountain bike riding..... here is a simple example, relax and drop your hands to your side....and then just lift them up....the natural position for your hands is palm facing the body

but handle bars are easy to change.....doesn't look like you can lose with either of these bikes.

I am not sure about the suitability of the Cheviot for IGH, the drop out does not allow for adjustment, so IGH would not be as clean. I have never gotten the feeling that Grant Petersen was an IGH fan.

I'm sure the Riv is an awesome bike. Good point about the dropouts, there are solutions, but they are not ideal for a fixed chain length. OTOH, for geared bikes, anything other than vertical dropouts is a bad idea

My wife has a Glorious (two generations earlier than Cheviot) and it's just beautiful. I can't say anything about the ride, it's too small.