Can't really advise you on which model to get as I'm unfamiliar with Cervelo. But I must say that of the two, I like the looks of the S2 more than the looks of the R3. Maybe that is just the color on the web page. At first I thought that the S series were their TT bikes and you were comparing apples to oranges. Hah, what do I know? (Those seat stays on the R3 sure are skinny.)

But ... about twitchyness ...

I have been riding a Mondia since 1972, a Reynolds 531 bike with Campagnolo Nuevo Record, and had been quite happy with it. Since then, the technology bike world passed me by. About a year and a half ago, I went out and purchased a Trek Madone. Carbon FIber! "Cool", I thought. What was very unsettling was its twitchyness. I just couldn't steer that thing straight, no matter how much I tried. I would have been a total disaster if I tried to ride in a pace line. No way was I going to ride hands free, even for a few yards like you see the first place finisher in a race do. I would go down for sure. That old Mondia ... boy, that thing sure was stable.

Advance a year, and I purchased another CF bike this Spring, this time a Kestrel that has a lot more aggressive geometry than the relaxed geometry of the Madone. Wow! I thought the Madone was twitchy. After riding the Kestrel, I came to realize that I adapted to the Madone and while I still will not ride hands free, it doesn't feel twitchy at all, unless I allow it to be. Like a wild stallion that you trained. It will respond to you, but will never be rid of its wild nature and tendancies. Now, it is the Kestrel that is the wild, untamed stallion who has a mind of its own. Two hands all the time on that baby. (But that thing sure can climb. I can just mentally will it to go up a hill, and go it does. Okay, I exaggerate, but you get the idea.)

All this is to say that you will get used to twitchyness...probably. And, that there are various degrees of it. Some of it can be mitigated by using different tires, a different sized stem, where you have our weight on the bike, etc. Those are nice looking bikes. If I wasn't happy with my Madone and Kestrel, (and with Pinarello frame in the closet, waiting for components), I'd seriously consider a Cervelo.