Memory shouldn't be an issue, your 1333 is fine. The i7-920 only runs up to 1066 stock, everything above that is an OC. And you can set multiplies to cut the OC to something manageable. Anyway with triple channel memory and large cache, you don't see a benefit pushing memory on i7-920.
Here's a fun reference. There are a million others for i7-920 OC'ing. (FWIW This post typed on an i7-920 at stock clock, hyperthreading disabled). http://www.overclock.net/t/538439/guide-to-overclocking-the-core-i7-920-or-930-to-4-0ghz