Road/TT Bikes Alternaives

I am a newbie cyclist and a newbie triathlete.

My current bike is an MTB, a Giant NRS3, but I am developing a liking for road biking. I am 5'6" and overweight at 174lbs though I plan to lose 10-15 more pounds in addition to the 40 I've already shed since starting triathlon training.

I can spend up to US$2k on a road bike and have been looking at models that can switch from classic road geometry for long rides to TT geometry for triathlons.

I have spotted only the Cervelos for this and I am considering the Soloist with 105 components or maybe even the P2K with Ultegra.

Questions:

1--What other models should I consider from other brands?

2--Where I am, Giant carbon road bikes can be had for a good price. Can I take such a bike then fit it with changes for when I need a TT bike or am I limited to bikes that were meant for dual-purpose road/TT use?

3--Articles (Sheldon Brown's, stuff from www.SlowTwitch.com) I've read mostly point that I'd benefit from 650C tires. Given my height and riding requirements, what are the arguments for 700C tires?

Thanks!

while the soloist would be a good choice, you can make most any traditional road bike into a serviceable tt bike. all you really need is a set of clip-on aerobars. however, a seatpost that would move you forward would be additive, especially for triathlons where the bike to run transition would be easier. before getting a tt bike, I used aerobars and a thomson setback seatpost fitted with its own saddle. turn the seatpost so it is "set forward" rather than back. when it came time for a tt, I just switched seatposts and mounted the aerobars. quick and simple. mine was a traditional geometry bike with top tube parallel to the ground. thomson makes a mtb version of the setback, 330mm I believe, that would probably work with a compact (sloping top tube) frame.

oh, and I'd go with 700 wheels. 650 tire/tubes can be hard to find if you're in a hurry.