5870 is about 60-70% faster than the 4870 in contemporary games on average - I imagine in more complex games using newer features that margin would widen.
5850 can only really be speculated at as less has been revealed about it, most of the specs banded about show the core being around 18-20% slower than the 5870 but crippled by a slower memory speed bringing it down to anything upto 40-50% slower depending on the final configuration and how sensitive to memory bandwidth it turns out.
5850 can only really be speculated at as less has been revealed about it, most of the specs banded about show the core being around 18-20% slower than the 5870 but crippled by a slower memory speed bringing it down to anything upto 40-50% slower depending on the final configuration and how sensitive to memory bandwidth it turns out.