I ride an '07 comp, and was in my LBS today and noticed an '09 or '10 Roubaix comp. I was amazed at how much bigger the downtube and BB area is with the newer designs, so I'll bet coming from the aluminum frame '06 version to the '10 comp would be significant.

One point to note, the '10 comp has 7r carbon layup, compared to my 6r from the '07 model. The expert spec makes the jump to 9r carbon and also full Ultegra, for only an extra $600 in list price. I'd definitely give that some thought if you can stretch.