right now in my house I am running the following

nvidia 9800gtx (current main box card)
ATI x1900xt ( second box)
nvidia 7900gt (laptop)
ati x800pe (wife's non gaming rig)
nvidia 6600gt (daughters pc)
ati 4670 (home theater)

i've bought cards from both companies over the years, and yes the 285 is a better card than the 4890 but 10% speed for that price difference is NOT worth it, the 4890 is more than enough and a much better bang for the buck.