X58A-UD3R overclock question

Ok so I'm overclocking on a X58A-UD3R. I'm using Corsair PC3-12800 (rated for 1600mhz). When I use a bclock of 200 and memory multiplier of x8 (200x8=1600), windows blue screens within 10 seconds of prime95. If I lower the RAM multiplier to x6 then this problem goes away. My question is how can I get this ram to run at 1600mhz stably with a 200mhz bclock.
Voltages are (rest of voltages auto):
vcore: 1.3v
qpi/vtt: 1.3v
dram: 1.65v
ioh:1.3v

Any help appreciated!