Most likely the BIOS issue is not the problem. It is not uncommon for a board vendor to have different BIOS chips on the same board; which would mean different BIOS files. As long as you didn't flash the chip with the wrong BIOS, you are OK. As to the reason why the 300a is so slow; it does not surprise me. That chip (in actual speed) is hardly much faster than the one you already have. Second, a Celeron does not have the same cache that a "regular" pentium does. That in itself would slow some things down a bit. The only other thing you should look at is if you have all the settings and memory timings correctly set in the BIOS. Perhaps something might have been set wrong there. Maybe you had the Celeron running at the P266 speed. In that case it would definately be slower. In the long run though, you will not see much, if any improvement with only a 33 MHz increase; especially if it is a Celeron.