this cpu is ONLY unlocked for LOWER multipliers, so its not a true unlock
this is what I did to overclock 6400+ BE
first: i tested fsb (rasing fsb by 5mhz each time), at 9x multiplier i believe i could get around 330/340 fsb
second: i raised the multiplier 1x and tested max fsb for each multiplier
...at this point i noticed that this cpu (at least mine) 'prefers' odd multipliers, the highest bootable fsb i got with an even multiplier was 235 (at 10x), wheras with odds i was able to boot with 240+ at 15x
note: i graphed all my results in excel (with a cheap laptop) using excel i found my highest clocks were 15x245fsb and 16x219fsb
third: i tested both 15x and 16x with prime95 till i found the highest stable clock, which for me was 15x234fsb
for this i started with the highest bootable clock and worked down in 5mhz increments, testing each with ~2hours of prime95
hope this helps, dont forget to play with the vcore. i found 1.4500 - 1.4875 to be ideal.
right now mine is set at 15x230fsb for 3.45ghz, with vcore at 1.4750
not all 6400's will overclock like this, maybe i got lucky. also, this was my first attempt at overclocking so my method might not be the best out there. good luck