The 4890 costs around 175 Euro, which is 50 Euro more than the 4870.
Ofcourse, the 4890 has twice as much memory and is about 10% faster. In my opinion, that's a pretty bad deal though.
Also, on my new system I only want to run on Win XP Pro as I have several older programs that do not run well on Vista.
As XP recognises 3GB of memory max, a videocard with 512MB is plenty.
But thanks anyway.