Oldfart should have a more definitive answer for you but the extra cache of the PIII's will allow them a performance advantage. However, the new 1.0A and 1.1A Cely Tualy's are essentially Pentium III processors now with a Celeron name. They have double the cache that the standard Celeron has and the same as many of the Pentium III's'. For example, my Pentium III 550E has 256k cache, and so do the Cely Tualy's. In general, the OC'd 1.0A Cely running at the same spead as the PIII 1.4 ghz, will perform in the same ball park and will not have the same disadvantage as the older 128k cache Celys.