Since I've sold that 6600, I'm strongly considering popping the Celeron into my motherboard with water cooling and seeing if I can blow a hole without removing the heatsink. It probably won't happen, but at least I'll be able to try again and take it further if necessary.
Since I first got it, it has been in two computers at stock clock speeds and in one other PC at 3.47GHz. It'* now back in my hands and still functioning. What do you predict will be my max overclock?