OC'ing an E8400 (Biostar TP43D2-A7 motherboard) help!

Hi to everyone in the forums, I´m trying to OC my e8400 but I can´t go any higher than 3.78GHz (420 FSB). All voltages are set to auto, I´ve tried to change the memory and core voltages manually and doesn´t make any difference. My RAM is Corsair XMS2 800MHz CL5(2 x 2GB). Does anyone know what can I do to go higher??? I was hoping to get at least 4GHz, but I don´t know if it´s possible with this motherboard. Thanks in advance for all your comments.

I´ve already set the ram voltage to 2.2v, change the core to +15% and nothing. Could be the ram limiting my OC. I been thinking in change to this one http://www.newegg.com/Product/Prod [...] RPR10664GK
What to you think?

set the fsb to where you eventually want it and run memtest 86+ to see if the ram is instable

hi again, I´ve tried the 6multi, any value greater than 420, no post.
changed the NB/SB voltage to +.3v (the maximum available), no post.
kamkal, can you go higher than 425???
any other sugestions? and thanks again for your comments.

yea id def say its ure ram holding you back, i had the same kit and had to swap for some pc8500 when i switched to my e8400, see if you can borrow a friends ram and try to see if you can get to a higher fsb with the 6 multi.

by lowering the multi to 6 allows you ro reach higher fsb yes this will lower your oc but your only trying to find the max fsb, if the max fsb is the same for the 6 and the 9 multi then its safe to assume its youe ram holding you back.