For our manual overclocking tests, we used MSI Afterburner. Our best results are as below.
Nvidia Founders Edition (220W power limit):
Gigabyte Windforce OC (216W power limit):
Palit Dual (200W power limit):
All three GPUs overclocked to similar levels. The Palit Dual is locked at 200W for the power limit, so it was typically behind the other two cards, but in most cases we're not looking at huge gains – 6-8% was pretty typical.
Interestingly, only the Founders Edition saw a real increase in power draw as a result of the overlock – it was up by about 13W. The other two cards barely increased their power consumption when overclocked.