Race vs. comfort geometry road bikes?

I'm shopping for a carbon road bike (under 3k) and everyone keeps asking me if I want a race or a comfort geometry. Comfort sounds better, of course, but I wonder what I'm sacrificing for that (weight, speed, possible aches and pains, etc?). Can being in a more aggressive position be comfortable for long periods of time? Or are there any bikes that are a nice balance between comfort and race?

Try the race bike. If it hurts to ride it, will you be happy?
It often depends on your age. Gals in their 20's can get away with being in really awful positions and not mind, but if it were me, it might even throw my back out. You have to see what works for you.