In my previous post, I gave very subjective info. Let me put it in more concrete/quantifiable terms so that it might help.

Comparing 2009 TCR alliance1 with CAAD9-5

Ride quality: Smoother with TCR
Fit: A wash. C'dale 58cm and Giant M/L both fit well. .
Components: Same. 105's.
'Lively' frame:105 by a mile. CAAD felt fast but totally dead.
Esthetics: Preferred the CAAD9-5 by a mile.
Stability: CAAD felt more twitchy. TCR is more stable.
Cornering: They both hang on in corners and communicate their limits much better than a Fred like me could ever utilize.
Stiffness:I feel no flex in either frame when cranking hard.
Patriotism: Handmade in the USA is one of the sexiest things I could ever hope to see on a bike. So CAAD is the winner here.

Subjective: I've fallen mady in love with the ride that the TCR provides. It was a very close choice between the CAAD9-5 and the Alliance1. I went with the TCR because of my perceived vast ride quality improvement. The CAAD felt dead. The TCR jumped to life like a startled horse when I stomped on the pedals. It cost me a couple hundred $'s more. But it was well worth it. That frame is just awesome. Oh, and it doesn't look quite as bad once you put on black bar-tape and saddle.

My reasons for going with the TCR are very personal. it was the bike that "felt right" to me. Test them both out and see what speaks to you.