I'd say the 4890 is better myself but then I would as I am buying one, I think others would agree with me though.
We're both between a rock & a hard place really what with the new releases just days away but mine is a cost effective upgrade which made up my mind & I am helping a mate out by selling him my 8800GTX, Horses for courses & all that.
I can say though I am No fanboy when it comes to GFX cards though & just buy the best bang for buck I can get at the time for the right price, Like I said this upgrade will cost me 55 quid.
I am also a bit long in the tooth for Guinea pigging new hardware & drivers & have just about had enough messing about finding solutions to the latest problem/bugz etc
I like buying cost effective upgrades of Decent hardware that has already been tested irl by others on here. I game & like to know for certain that whatever hardware I buy will do what I want Before I actually buy it.
On top of that even though I have 300 quid laying about I prefer to use it for other toys.