i have a PIII450 week 28 running at 558mhz for about a week now with no problems. I haven't tried to go any higher because i only have generic pc100 and the standard heat sink/fan. I will be getting an alpha cooler and ram (if it ever goes down in price again!!). It's running on a Abit BE6 at 2.0v. I imagine with the ram and cooler I could get higher, but it's stable here and kicks so I might now screw with it..