i'm using the 1GB stick instead of the 2GB kit you've got (so it's essentially the same ram) and i've heard that the ram can hadle up to 2.4V but the G.Skill only says up to 2.1V to cover their butts.
I was having the same problem as you and then i set the voltage to 2.2-2.3V and it was stable @ 950mhz 4-4-4-12 timings but i don't have any real reason to push it farther yet.
my suggestion is to up the voltage a little. BUT do it at your own risk and understand that it will probably (i don't know why it wouldn't) void your warenty with the manufactorer.
i've heard that people can reach DDR2-1016 @ 4-4-4-12 fairly easily with voltage at 2.4V if that helps at all.
Antec NeoPower 650W
Intel Core 2 Duo E8400 (w/ Arctic Freezer 7)
4GB DDR2-1000 G.Skill
Sapphire x1950 Pro 512mb (w/ V700)
250GB, 500GB and 1.5TB Seagate Barracudas (2.25TB total)
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