I'm looking for something similar to the OP and am kind of stuck, because I've been out of the loop on video cards for quite a bit now. Essentially, I think my 8800GTX is buggered and I'm probably going to RMA it. But frankly, I'm thinking about replacing it as well. The 4870 caught my eye and especially ASUS' model, because they have a $30 rebate and I can get it for 239.99 after rebate (only $40-50 off the 4850). Some benchmarks that I've peeked at showed that the 4870 is faster than my 8800GTX and my most rigorous use of my video card is playing two "instances" (note, two applications running at the same time) of World of Warcraft at 1680x1050 with most settings at high (AA and AF are not).
My biggest concern with ATi has always been their driver support overall (this mainly was on peripherals), but how is the CCC these days... pretty rock solid overall?
Any thoughts overall? If you think the 4850 is a better choice even with the somewhat tough beatings I put on my cards, then by all means, let me know
. Also note that the new expansion coming out later this year will be a bit more hard on graphics cards as they're adding in better shadow effects, so taking that into account may be better to.