The new bike feels good, but candidly, I haven't spent enough time on it to get very specific.

The biggest change (immediately noticable) is the improved fit on the new bike. I was, in fact, considering upgrading the drivetrain on the 2100 and marching on for a bit longer, however, while going through the process, it became VERY readily apparent that there was a ton of room for improvement in terms of fit on the Trek. The 2100 was my first road bike and it has become clear, now, that I was not as well prepared/informed , then, for the buying experience. I ended with up a 54cm frame when, in hindsight, a 52cm frame would have provided a much better fit. i simply didn't understand the importance of fit and it seems that the the LBS probably had a 54cm Trek that they could "make work" when in reality 52cm would probably have been the much better choice. That LBS has long since gone of out business. The fit specialist at the new LBS is excellent and walked me through all the shortcomings of my Trek (from a fit perspective only). And, yes, in this case I was careful in terms of "drinking the kool aid" to make sure I wasn't being "sold" by a fit guy. In a short time it became clear that this person was not out to try and sell me and everything he was saying made perfect sense. He even tried to improve my fit on the Trek, however, once I jumped on the CAAD in the right size, there really was no going back. Despite the CAAD having a more aggressive geometry it is significantly more comfortable thant my Trek simply because it fits a WHOLE lot better. Call me a noob, but I never even realized that was unable to comfortably grasp the shifters on my Trek for extended periods of time without experiencing fatigue relatively quickly and moving back to the outer curve of the handlebars (the reach was simply too much for the length of my torso). Additionally, I was also essentially "running into myself" when in the drops on the Trek. I was initially a bit concerned that the CAAD 10 geometry might be too aggressive for me, however, post a proper and thorough fit process, it has been a wonderful improvement.

The Trek 2100 was triple (52/42/30) with a 105-5500 series FD, Ultegra-6500 RD, SRAM 12-25 cassette and 105-5510 shifters. The CAAD 10 is set up with a compact double (50/34) and a 12-27 cassette. The drivetrain is significantly smoother on the CAAD vs. the Trek. Additionally, I find myself having to "mash" significantly less than I did on the Trek, where the middle ring on the chainset was a 42 (somewhat tall) and the "granny" was a 30.....i.e. no comfortable middle ground.

I don't like the Tektro R580 brakes on the CAAD 10/5. I seem to be having some grinding issues on the front brakes. I'm being told that the cable length pull on the 105-5700 shifter requires the Tektro brakes to be mounted very close to the wheel rim, which can result in some rubbing if not adjusted perfectly. Whether there is any truth to that; I cannot say with certainty. I was planning to swap the calipers out for 105 from the start anyway, so we'll see what happens when I make the change. By the comparison, the 105 brakes on the Trek were top notch with nary a squeak.

The CAAD definitely feels lighter and along with the improved drivetrain, feels more responsive.

Thats all I've got for now.