You would have to overclock both the CPU and the PPU; and it is the PPU that poses the problem. If you don't overclcok the PPU your games will still run slow, but if you do overclock the PPU it will generate a signal that has PAL timings scaled to 60Hz. Now before you say "that's what I want" I should point out that signal does not conform to any standard, including PAL 60. I also don't believe the NES has a separate color crystal which means that the color burst frequency would be incorrect resulting in a black and white picture.