http://www.overclockers.co.uk/acatalog/7900_Series.html
4th from the bottom.
I actually got sent a Palit card, now running at 580/1450, the core overclocks very well but gets rather hot coming up to 600MHz and the memory is good for just over 1400MHz, which is what you would expect for samsung 1.4ns memory rated for 1428Mhz at its standard operating voltage.
Core will run upto 625MHz but not for long as the heat climbs rapidly and stability fails at about 70c at that speed.
Its not really worth buying a bigger cooler unless you already have one as for £50 more you can get the 7900GTO which clocked higher and has a 24pp8vs config.