Your first point: It's going to be hard to get 920 stable at 4.2 GHz. Be thankful you have 4.0. Most people with a 920 have to settle for 3.8 (for a 24/7 folding overclock). As for your second point: I don't really know. In general I advise against messing around with priority. I do know that you can get some improvement by installing a RAM disk. Others on this forum have done so and have reported good results.