I think that you're asking for trouble trying to carry heavy weight on a fancy road bike. The carbon frame will probably stand up to it, but I bet you have very low spoke count wheels that will not handle the weight very well.
The carbon frame will *definitely* stand up to it, as they are tested to standards identical to or exceeding those of metal frames. The wheels will hold up just fine, especially considering OP + max rack load will still be lighter than many riders alone.
sauce: I work with a few hundred people who commute on carbon fiber wunderbikes and fancy lightweight wheels, many of them with racks of some sort. Also plenty of personal experience loading up my 18H front / 24H rear with close to 275 lbs me + bike + gear, then rumbling down washboard National Forest Service roads.
Race frames have chainstays that are very short, so if you do get something that lets you mount panniers back there, you'll probably be kicking the bags with your heels as you pedal.
Except that small people bikes have the same chainstay length as big people bikes, while small people have smaller feet that allow heel clearance at that length. Aside, there are plenty of bag options that accommodate for this.
You could try something like a frame bag:
ew gross
Most peeps at work use one of these, mostly because they're cheap when you don't have to pay retail. I'm sure there is a cheaper/better option somewhere but at least this isn't $200.
http://www.bontrager.com/model/08214If you have a rack laying around that you aren't using, or want the option of installing a cheaper rack on the road bike, you can get the dropout adapters and brake mount adapters for the above rack separately, part #'s 428715 and 431021 respectively
http://www.bontrager.com/model/08181There's also seatpost-mounted rack bosses, which will be a little stiffer than the single brake mount point.
http://www.bontrager.com/model/08427as far as weight is concerned, those seatpost mount racks are usually about 20 lb. max, which means maybe 10 before they start to get wiggly. Above setup has a listed max weight of 50 lbs., and will start to get wiggly around 30, which also happens to be right about where your handling gets mildly messed up from the front / back weight imbalance. Imbalanced loads are not a problem unique to road bikes though; it will happen with anything without a front rack. If you want to use the full 50 pounds more than once every other week I'd say go ahead and look for a trailer.