The guy in the LBS suggested that by swapping out the stem, I could get most of the advantages of the SR800 in the R700 which is both lighter and faster but costs the same. I am finding the more comfortable road bikes to be not that much more comfortable than the performance models so I am inclined to believe him. The CAAD8 bikes definitely feel faster and more fun so they may make more sense from a getting exercise point of view. I should probably try harder to get my wife more into biking and have her get a bike that could take a rack (sort of a 2 wheel SAG wagon).

Your choice of the R900 brings up another advantage of the R series. Lots of choices for components and wheels. How do you like the Mavic wheels on the R900? The LBS guy was a big fan of the Mavics though he thought the 550s would be fine. I assume you bought the 900 because you prefer Campy components.

For comparison purposes, I test rode the R1000 back to back with the R700 on a second visit. I had to have the shop adjust the shifters for the R1000 but once the did the shifting was a bit nicer than the R700. The Ultegra levers were much nicer than the 9spd 105s on the R700, I have large hands so I liked the larger hood grips. The 10sp 105 levers on the R800 seem much closer to the Ultegra/Dura Ace design. The R1000 seemed stiffer to me. I am not sure if this was the different front fork or the wheels.
The most dramatic difference I noticed was the brakes though. They seemed quite a bit better on the R1000. They could have been better adjusted or it could have been the Ultegra brakes vs the Cannondale house brand (any idea who makes the Cannondale brakes?).