I'm looking to get a touring bike this spring and hopefully do a trip in Europe late summer. My past: long time MTB rider, switched to singlespeed road bike last year... love it (Fuji Track).
The touring models I'm looking at are: Trek 520, Fuji World or Touring, Cannondale T800, Devinci Caribou 1, Surly Long Haul Trucker.
I've whittled it down to Trek 520 and Surly LHT... just going by pricing, features and user reviews online.
For fun, I compared my current bikes' geometry to the Trek 520... and I'm surprised how close the numbers are. As far as I can tell the major difference is 5cm more on the chainstay, which also means 5cm more wheel base. Is this really enough to make the ride feel different? Granted, also, that the handlebar setup will be different too (higher on the Trek 520).
Here is an image showing my current bike (Fuji Track) and the two closest comparable Trek 520 sizes.
Rocky Mountian builds great bikes-- I'm glad to see them venturing into the touring world. It's great to see them come up with a different style bike, and just not another 700c classic touring bike clone.
One thing to look at would be frame weight, not because the weight is in itself a big factor, but because it may highlight different tubing choices. One would expect two bikes even if Identical in every way geometry wise, to have very different tubing when intended for such different purposes.
I don't think the 2 inches in the stays is all that big a deal. Longer stays are pretty much an advantage on almost any bike. Maybe not on a racing bike, assuming you are a real racer, not just someone who rides racing bikes. If you really live in the pack, and need razor sharp handling, that's one thing, for most other road uses long stays are an advantage, and they can be lot longer than +2 inches, try +10. As long as you can get heel clearance for the size of paniers you are carrying, stay length is not a deal breaker. On one end of the extreme there are all the folks who use hsort stayed MTBs, on the other there are way over length frames made by the likes of Thorn (special order), Sakkit, Arvon, LHT Big Dummy.
So the factors you want to look at are geometry yes (stearing geometry is way important, not just CS length), but also tubing, brake set-up, fork, hub width, braze on's, fender accomodation, rack accomodation. For instance stand over can be important on a touring bike where sometimes the junk out back makes it hard to swing a leg over. A stand over that might be fine on a bike without any rubish back there used on a track, is all of a sudden a ba!! breaker if you have to hop down on the bar on a rough trail section. Often half to 1 degree less seat post angle is adviseable, particularly with the Brooks.