From what I could find it would overheat on the stock cooling.
The ones I did find had part of the bottom cut and an extra fan ,or on some 2 fans mounted to the bottom of the laptop for extra cooling. Otherwise it will overheat and throttle down. But that kind of takes away from the portable aspect of having a laptop.
The 6970 is a drop in replacement. Anything faster or newer would require cooling modifications.
Going from a GTX 260 to a GTX460m or ATI 6970m is a big upgrade. Both are plug in with no modifications needed.
If you want to try more it is a risk you will have to take. I can post links to mods and information if you decide you want to take the risk.
Me or Toms hardware can not be held responsible for supplying you this...