Best practices for OCing an i7 920 would be to Turn off Speedstep, Turn off Turbo, and set the CPU ratio to 20. Some people will say turn off Hyperthreading, but its a GOOD performance feature and I wouldn't want to disable it. You will get a higher clock, but you loose the hyperthreading ability.
I would start by setting the vcore to 1.2v which is stock and seeing if it will boot with a BLK or 190 (190x20 = 3800MHz) If it does not, bump up the voltage to 1.25. If that runs stable and after stress tests, you can try 1.225v if that is not stable, stick with 1.25. If 1.25 is not stable bump up to 1.26185V or whatever it is.
Personally I also set my Memory to use the XMP profiles. This set my vDRAM to 1.6, I believe stock is 1.5 and "max" for an i7 is 1.65 (per intel specs). I set my QPI to 1.2v which is stock as well.
Just watch your temps using coretemp or something like that. I use OCCT 3.0.1 with custom settings as follows for an hour: Large dataset, High priority, Hyperthreading ON.