I ran TWO systems with Cel 433s at 540 very successfully BM6 MBs. Sufficient CPU and Case cooling is absolutely necessary. I then upgraded my Abit BM6 motherboard Bios and stuck in Cel II 633s that are still running at 880. I am using a 3DFXCool LilMoFo fan and heatsink in both systems. Celerons are indeed worth overclocking. Why not, if you have the chips, the extra speed is free! Just so you know I am not too one sided, I also have a third system with an AMD Tbird 900 overclocked to 1000 (and rising), with an ABIT KT7-Raid motherboard and two Maxtor 30GB in raid stripe configuration. I will say that if you are going to buy/build from scratch, the best bang for your buck currently is the Duron chip which also overclocks well.