I have an 05 Specialized Roubaix comp. I am thinking of a new bike this year and I will be looking for just a frame set, since I just put a new 2012 SRAM Red group on the bike late last summer. Will probably want to get frame first, and build up bike using my current parts. Then, later down the road I will upgrade wheels, bar, stem, etc. I'm middle aged (47) and not getting any younger or more flexible so I definitely want to stay with a "relaxed" geo bike, at least a bike with a somewhat taller head tube. Also want top of the line carbon frame for sure; not considering any other frame material at this time. Light, stiff, fast, and fun!

Obvious choice would be another Roubaix, if that's what I do it will probably be an S-Works SL4. I'm also aware of the Trek Domane, and would definitely consider one; or an h2 or 3 fit Madone. Another bike I've become aware of that sounds interesting is the Focus Izalco Ergoride. It was highly rated in a magazine review I read, but I don't know if it will be up to par with an SL4 Roubaix, but it'd be quite a bit less $$. What about Cervelo? I heard or read somewhere that the R3 and R5 have taller head tube. What other similar bikes are out there that I can buy as frame set?

What is your budget? You might take a look at Calfee, Parlee and Crumpton they build hand made and custom frames in the US.

Thanks but the S-Works Roubaix is the upper limit of my budget!

Take a look at the Cervelo RS.

Edit: looks like the RS has been discontinued for 2013. The R3 would suit you well though.

Competitive Cyclist is hawking their last year's frames... might want to see what they have on hand.

I didn't ride the S-works Roubaix, only the Expert in the current model. Then I test rode the Focus Izalco Ergoride, and to me the Focus felt stiffer and better for power transfer when out of the saddle (I'm not a lightweight) yet still very compliant on bad pavement. So that's what I ended up purchasing. I still like the current Roubaix better in the looks department, but I'm happy with the build quality and price of the Focus. YMMV

Also consider the Scott CR1.

C'dale Synapse?

I'd go with another Roubaix.

Hard to beat a roubaix.

For custom carbon, the Crumpton SL is sweet, frame is five thousand, three hundred dollars. Goes up with options like hidden cables.
For rack bikes, I too like the Cervelo R5, but their site has the frame for $5,000 but also list a complete R5 with SRAM Red build for $5,900. The Cervelo R3 frame on their site is $2,200, $3,800 for the R3 Team Ultegra model. Both are above your price range, but interesting for comparison sake of complete bike price versus just the frame price. I guess there may be deals for these cheaper than their site price, don't know myself.
Cannondale has a super light frame for the Supersix models and an even lighter one for the Supersix Hi MOD road bikes. Cannondale Supersix 3 Ultegra costs $3,350, Supersix Evo Red (lighter frame) is $4,450. Supersix Evo Ultegra Di2 is $5,200. Cheapest Hi MOD bike is the Supersix Evo Hi MOD Dura Ace for $7,990. I don't know much about Cannondale bikes, but my LBS carries them. From what I see on their web site, on some models, they use their own Cannondale brand of stem, seat post and cranks. Whether they are good/bad/eqaul to others I cannot say. There are many Cannondale enthusiast on this board, maybe some of them can chime in here and give you solid answers where I don't have any. First question is, can you buy an Evo or Hi MOD frame? Don't see one listed on Cannondale's site. I have seen some on Ebay, but I would personally rather go through my local dealer if I went that route. If anyone knows were you can buy a 2013 Evo or Hi MOD frame, I would want to know too.
The higher end Supersix Evo Hi MOD bikes are costly and imho have ugly color schemes. The Evo Ultegra, Evo Red and Supersix 3 Ultegra can be had with a decent blacked out frame.

I like the Roubaix a lot and an S-works would be sweet if you can snatch one up in your budget range. Only thing I would look at personally would be a Synapse or a Hi-Mod, as the reply above suggests, an Evo would be really nice, too, but that is me, YMMV. I will look at the 2013 catalog I picked up and see which frames are sold bare when I get home from work.

Bill

I like Crampton too but Calfee and Parlees are cheaper. Calfees range from $2100 to $3800 I think. Custom would be more.

The clymb has some great deals on a few parlee's for another day. Might be worth checking out https://www.theclymb.com/brand-event/3335/Parlee

I'd go with the Roubaix too. In fact, I am getting one in the next few weeks. I haven't ridden a nicer smoother bike yet.

A guy in my club just replaced his Roubaix with a Cannondale supersix evo. One thing he said is that he noticed less flex in the supersix when sprinting or standing on a climb.