yep sounds like the 400fsb of the celeron is holding it back (100mhz real terms) as running the
ram at 266 (133 real) is already async by 3:4 (fsb:memory) your board will have a few of these ratios but they are mostly there to slow the
ram down rather than speed it up. such as 5:4, 4:3 and 3:2 dividers. This is because of the p4's high fsb would require ddr400 to be in sync. so they've built in these options so you can run ddr333, 266 etc. It's a bonus that you can slow down your
ram whilst overclocking as well.
As on the release of the P4 'C' (800fsb) ddr 400 was about as fast as it got. When i got mine a few weeks after launch i got some ddr433 crucial chips but with such a large overclock i use a 5:4 diveder just to get the
ram back down to ddr433 :-)
K