I just volt modded my 8800s from the stock 1.0 to 1.1, and am running stable at 700mhz core/1000mhz mem. By having my CPU at 3.0ghz, volt modded down to 1.375 from 1.475.
Anyway, here is +1 to 8800s running at 700/1000!!!!!
Just to be safe, I dropped my clocks to 680/950 and have absolutly no issues at all. This is proof, that our cards need more voltage. When running at 1.0v I was only able to go up to 645/950 before getting errors and crashes. As soon as I gave them more voltage, I was able to run the cards at as high as 740 at 1.15 volts, but heat became a problem. I could solder an external heatsink, but what would be the point, this is a laptop. Basicaly I wasn't able to find a limit as to how high these cards could go. They took anything that was thrown at them. With proper cooling and maybe even a laptop cooler, one could go higher, but with stock cooling, I find that 700/1000 is the absolute limit. 1000 being the mem limit regardless and 700 being the GPU limit given the heat issue. Provided better cooling, these cards could run close to if not at 800mhz at 1.15 volts.
@abadee, 1.15v at 800 is something you may want to try with your AC duct, but I'm good with what I've got so far.
I'm running mine at 680/950 and the cards are taking it just fine with no errors in ati tool, not even the yellow dots you get before errors are seen. Nothing! This proves, that errors people are seeing with these cards are simply due to the cards running out of power.
Look at this post for more info on how I discovered that the voltage being fed to the 8800s via their BIOS' was not enough to power them beyond 645 or so.http://www.notebookforums.com/thread217172-4.html
I get ~14.5K running on an X7900 in vistaX64!!!!! An X9000 as Abadee has and others would easily break above even 15200+ without any external cooling. The X7900 just can't run cool enough at 3.4ghz without throttling and the voltage reduction required to keep it from throttling is just too great to have it run stable; so I'm stuck at 3.0ghz at 1.3750 and the 8800s at 680/950 at 1.1v.
Happy Overclocking and 15K + 3dmark06 scores.