ASUS P5B-Deluxe; Problems & Fixes

[Bhairava]

Hi to everybody. I just bought a corsair 4gb kit TWIN2X4096-6400C4DHX and i have problems on P5b deluxe.
This is my system:
e6300
p5b deluxe wifi
enermax coolergiant 600w

My system is rock solid on 460x7 with a very cheap Kingston 2x1GB kit.
I tried the new rams: one 2gb does not go beyond @900, the other one reach @920 (at @930 i get erros, at @940 i get BSOD). Memtest by floppy does not give any problems at @930, it finishes one full cycle on 460x7, but Memetest in Windows and Orthos get a lot of errors.
I set the mobo in this way:
vNB: 1,45
vRam: 2,3 (Corsair recommends 2,1 on default frequency)
letency: 5-5-5-15.
I read a review about the cas5 kit, and it reaches @1066, mines are cas4, so they cannot stop at @920.
Do you think it's my mobo?
Can you help me?
Thanks.