Why wont my 1600 ddr3 run at 1600?

No matter what i do i cant get my mushkin radoactive enhanced (2 x 4G) to run at 1600Mhz regardless of how slack i set timings. Am i right in thinking this could be down to my CPU (AMD Phenom II X6 1090T BE) and motherboard (ASUS M5A99X EVO AMD 990X) choice? I have no problems at 1333Mhz and even run stable with the timings as tight as the motherboard will let me. With timings this tight at 1333Mhz would i actually see any performance boost if i was able to run at 1600Mhz with the spd settings?

Use the same memory divider but run the FSB at 240MHz (you'll need to drop CPU multi). I bet you hit 1600 then.

I have tried using the the fsb to raise my memory frequency but again i can get to about 1500mhz with spd settings and no more. Have not seen any option in my bios to manually change memory divider.

The memory divider option is there, it may be called something else though - not familiar with your board.

What is the max FSB you have been able to hit?

This is what I would do:
1. Lower the CPU multi to 15x
2. Lower the CPU-NB and HTT multi, so those frequencies don't go above 2000MHz
3. Increase FSB attempting to hit 240 or more

Step 1 and 2 are important to rule out other factors, then you'll find your max FSB - then you can set the CPU multi and CPU-NB multi back to normal levels. Its entirely possible you weren't able to hit higher FSB before because your HTT or CPU-NB were getting too high.

did all the things u suggested even raised memory voltage to 1.6 and couldn't get the pc to boot, still cant find where i can manually changed the memory divider in the bios so i'm not sure if that's a problem when raising the fsb?

The "memory divider" options are integrated into the available Memory Frequency choices at specific HT Ref Clocks. In other words the available dividers are calculated by the BIOS, and are listed in the Memory Frequency field of the UEFI. So for instance at the default HT Ref Clock of 200MHz, and looking at the CPU-Z pic. you posted, although not seen in the BIOS the FSB : DRAM ratio is 3:10 = DDR3-1333. The DDR3-1333 option is an available choice in the Memory Frequency drop-down in the BIOS, but the 3:10 ratio option isn't seen because it's a calculated known value. So depending on the available DRAM multipliers, the Memory Frequency options will be displayed accordingly.

ok got it yes that's how i manage to get the ram to run at 1500 by increasing the fsb clock, are u suggesting that the 3 values i have represent the different ratios so is there any reason why a certain divider would be more stable than the other 2 or does it make no difference?

Yes, the available frequencies at a certain HT Ref Clock represent the different ratios. You should have available at a 200MHz CPU BCLK / HT Ref Clock these options to choose from... x4 (800 MHz), x5.33 (1066 MHz),
x6.66 (1333 MHz ), and x8 (1600 MHz). Since you have DDR3-1600 installed, set the multiplier to x8 = DDR3-1600 at a 200MHz HT. In order to run 8GB of RAM stably at 800MHz, you may need to bump the NB and/or CPU/NB voltages.