get stable on 4-4-4-12 and OC help

[PakaPaka]

hey

my G.Skill 4GB 800MHZ Pi cant get stable on 4-4-4-12 with my OC to 890MHZ.
is this is so hard to get this timing on 890MHZ? i think it will be easy for him..
the VRam is on 2.1V, he need more voltage to get this timing?

what will help me to get stable on 4-4-4-12 at 890MHZ?

tanks.