Sometimes up to 20
We got some rough Geforce GTX 580 performance figures and they indicate that the new card could be as much as 15 to 20 percent faster than the old GF100-based Geforce GTX 480.
This is something that we'd expected from the tweaked and fixed GF100 chip. The core architecture is slightly changed in order to make this GPU more efficient and to lower the TDPs, at least slightly.
The general idea was to stay at a similar TDP and get much more performance, per watt of course. Since this is one of the biggest chips ever built, or should we say re-spun from the GF100, you have to know by now that it will get hot and fast, but so do any of the products in this market range.
Also bear in mind that both companies still have dual-chip cards in the pipeline and they should end up even faster. If we only had such cool content to really need so much processing power.