Bob,
I have used IP on the 9800's for some time and find it a good RIP for most photographers. IP offers a number of layout tools, good free profiles, and a simple and efficient interface. Quality, aside using a RIP alters the way you work. In terms of quality, the profile is the key. Image print maintains a very complete and up to date catalogue of profiles that are free to users. The quality of these profiles are first rate. That said, if you are using good profiles in conjunction with the drivers I would think that, for color work, you would not see a substantial difference. BW I think is a different issue, I have found that the BW output from IP is about as good as it gets, and is generally much better than what you can get from the using the driver. As far as 8 vs 16 bit, I dont believe IP will accept 16 bit images. Regardless, editing in 16 bit is a good options, but in print it rarely yields any improvement. Hope this helps, feel free to ping me if you have any furthur questions.
Julian Mussi
www.spectraflow.com