vdd mod

I'm thinking about doing a vdd mod so that I can try to push my fsb higher and to make it more stable but I have 2 questions. First of all, what is the max voltage I can put it to, I'm using an vantec copper iceberg on the northbridge. Secondly, I'm gonna try the non-soldering method to start and I wanted to know if it would be a good idea/safe to use some non-permanent conductive grease that I have or would it be better to just go with the 2B pencil? Thanks a lot.