I’ve worked on all my bikes for many years. I just installed the new DA 7900 kit on my 2007 P3C. After it was fully installed- the shifting with the Front Derailleur was/is flawless and very, very smooth. No trimming needed for the full 10 gears when in the big chainring. The crankset weighed identical to my 7800 crankset… maybe I’ve worn down some of the teeth by a couple grams with 2 years of mileage and a new version 7800 vs a new version 7900 has the 7900 trumping the 7800 by a little bit. All other parts were definitely lighter- bar con shifters, brakes, FD, RD, chain. I also- put the jagwire Barcon 2.0 on in combination with the new 7900 levers to save some additional weight for minimal price upgrade- something to consider if you are rebuilding everything.
Anyway- as I said above- the front shifting was flawless- once everything was adjusted. The rear shifting, however, was working- poorly- with the harder smaller/harder gears working and then some of the easier gears were not shifting well- something highly unusual for new components- and often a sign of a bent dropout tab or something else being errant. I had installed some ceramic RD pulleys- but I didn’t think they would alter shifting- that much- or only alter half of the cassette block. I knew my 7800 shifted no problem (the stuff i just took off my bike). Also, the shifting seemed a little louder than the 7800. So I googled ‘P3C and 7900 rear derailleur’ and the first link that came up was this:
http://www.cervelo.com/...allation%20final.pdf Gotta love Google!
Anyway- on some? many? most? all? pre 2009 P1, P2, and P3s when installing the new 7900 RD- the b tension screw (actually- it’s the b tension bolt block in my case) can rub the drop out tab- limiting RD movement, and seriously compromising shifting performance. The PDF shows what to do- I ended up using some small hand files - (versus taking out the dremel- or using their hack job method- which wouldn’t/didn’t work in my case- b/c the b tension bolt block was rubbing- not only the screw). The solution just took a couple minutes to solve. I took her out on a 60 mile maiden voyage- and the new DA stuff is really nice. Is there a huge difference compared to the 7800- I’d say no. Is it truly worth the upgrade price- probably not. But- the highpoints in my mind- the front derailleur shifting is really, really nice. The RD appears to shift a hair better. The brakes are stellar- better than the 7800s. It’s a little lighter kit- about 100 grams or so I saved (including putting on the Jagwire Barcon 2.0s) Many would say Shimano had the standard for braking with their 7800 brakes. The 7900s are about 25 grams lighter and they adjust easier (7800 adjusted easily, too), are slightly smaller profile (maybe more aero?), and brake even better- a win-win-win combination. One interesting thing about the brakes though- is the cable adjusting bolt- where you can take up slack or decrease brake cable slack- the threads are reverse direction- which maybe is to decrease changes due to vibration- but a new idiosyncrasy.