me personally, i'm 5'7" with a 30" inseam and a long torso with wide shoulders. i'm riding a 52cm Supersix EVO with a 100mm stem and 44cm bars, and the EVO and CAAD have very similar geometries...

i have about 500 miles on that bike, and i will say i really like the fit and the size was perfect.

as far as the OP goes, i definitely think the 48cm would be too small, my mechanic rides two 48cm EVO's and he's only 5'4" with a shorter inseam than the OP. i think the only problem that you're going to run into with the 50cm is that since you have a short inseam, the stand over is going to be higher than you really want and you're not going to have that much seat post showing when you're done with your fitting. me personally, i have 80mm of seatpost showing so i can clamp it on my Park stand, but that's going to happen with the CAAD or the EVO because of their geometry. bottom line, definitely go with the 50cm and just work with the stem as far as the reach goes...