My thought from your original post was to compare the rides of the frames. A good composite frame will be noticeably smoother and make an aluminum frame seem like a torture machine on less than smooth roads. I think its worth $900 because I paid it on my bike. As to comparison of components, the 105 derailleur reached a level of quality in 2007 that is really good and should be suitable for all who would pay up to $3000 for a bike. Leave the Dura-ace for the $5000+ crowd. It is not that much better, just lighter.

Most manufacturers have been cutting costs in the 2007-2008 models by cheapening the wheelsets and substituting generic components at various points in the bike. The wheels are the most glaring reduction in quality - some of them are just plain junk.

When you go looking again, be sure to look at Specialized carbon roubaix and tarmac in the $2000 range. They are really smooth and will help provide alternative views to help you find out what you really want. I was advised to ride lots of bikes when I went shopping last year. I rode Trek, Guru, Cannondale, Specialized, Giant, and Seven bikes in price ranges from $1200-$4000. My choice became quite clear in terms of ride, performance, and budget. I bought a Specialized Roubaix. It just turned one year old and I have 5000 miles on it. I changed the saddle, the stem and handlebars. I just replaced the chain and rear cassette and had the bottom bracket serviced. It rides and performs like the day it was new. I am still very happy with this bike for my style riding.

Bob