920 and ram ocing questions

[Naff8000]

So I increased my i7 920 to 185x20: 3.7ghz. Increased the vcore to 1.35V and vtt to 1.34V. The cpu is still running surprisingly nice and cool.

My question is: how much more % performance would I get from 3.7ghz to 4ghz? I've not changed anything to do with my ram, is my ram now also fully overclocked thanks to the fsb increase? The ram voltage is still on auto, should I change that?
Ram is 6gb 1600mhz 8-8-8-24

Lastly what do the ram multipliers mean? I tried 12.0x and 10.0x. It didn't like that, so currently have it on 6.0x.

Any help is greatly appreciated.

 

[ETNiES]

From everything i've read ram multi should be on 6x or 8x so your ok there, mines on 8, cpu running at 3.8 x21.

 

[Naff8000]

I'm having real trouble getting a stable 8.0x on 185mhz BLCK. On 6.0x thats only 1110 mhz

Tried all the way from 1.5V to 1.64V

Does anyone know how much performance loss I'd see from just leaving it at 6.0x? If it's not much I'll just leave it.