For safety's sake, I wouldn't go much higher than 70-75 C. If you are going to OC your notebook, definitely clean the fans thoroughly. The loss of warranty due to really opening the case is no longer and issue, as you mentioned :p. If the temps don't drop much, then I think you won't be able to put a good OC on it, but if they drop dramatically, say into the low-50's, you could definitely get a performance bump.
The means to overclocking regardless of the utility that you use is to start slow and build up. Run the Windows Experience Index, or else some other graphical benchmark to stress-test the system and ensure stability. If the system hangs or the driver crashes, then back off on the OC.
Try a small (say 15 MHz bump to core [30 MHz shader]) and see what happens. If it is stable, add another 5-10 (10-20) MHz and repeat. Once the system starts to act up, back off--use common sense.
🙂 The memory also can be pushed, maybe 20-30 MHz at a time. Don't push the memory and the core/shaders on the same round, that way if something acts up, you know what the culprit is.
The whole OC game is a bunch of tweaking, and there is no better way to learn it than to do it. If you don't touch the voltages, there is no risk of damaging your system--though you could make it unstable till you reboot. Unlike CPUs, which require BIOS mods to overclock, GPUs are OC'ed by special utilities which are software-only mods. When the system reboots, the vBios will reset the clocks back to the defaults, so don't tell the utility of your choice to run at start-up until you have the system confidently stable.
Enjoy! Good luck! ASUS put out on the ROG site a nice little tutorial on OC'ing a desktop card, but the technique is the same.
Link:
http://rog.asus.com/96782012/graphics-cards-2/a-simple-guide-to-overclocking-your-graphics-card-with...