check your BIOS again.. naa nay SPD setting. usually in percentage related to CPU FSB.. if CPU FSB nimo is 333 put the SPD setting to 120% and not 100%. most probably ang ratio nimo naka set to 1:1.
your RAM will run at 480mhz if you set it to 120%.

Try relaxing your memory Latency, cause some RAMS have a very tight
default latency, and sometimes it even can't reach its default speed.
It also depends on the mobo na maka kaya og tight timings with
higher speeds sa RAM. In this case i think dili makaya sa imo MOBO ang tight timings.

Try to adjust your RAM timings:
FSBRAM - 1:1 / 100%
CAS - 2.5
RAS to CAS delay - 4
RAS precharge - 4
Cycle time - 11

call me @:
0916-4193711 - I can help you with it.