so core clock difference = 20%, and gains on the 4870 are rumored to be at best 30% faster than the 4850........
My prediction: GDDR5 Memory bandwidth is not going to make much of a difference, and when it does (very high res, aa, af ), the 512MB buffer on the initial 4870 cards are going to choke. Maybe its better to wait for the 1GB variants if you are set on the 4870