Seems that it is more of a cooler issue than anything else. Possibly to stop them being overclocked so easy as to reach 4870 levels. BTW, the standard paste was replaced by one reviewer and it dropped the temps by about 15 degrees! Certainly not to be sniffed at, and with better fan control or additional cooling I think they will be good to play with 
I think what it really comes down to is how good GDDR5 turns out to be, and whether it is worth buying the 4870 for that reason?
Matthew

I think what it really comes down to is how good GDDR5 turns out to be, and whether it is worth buying the 4870 for that reason?
Matthew