Do a fresh boot, shut down any extraneous applications/processes, make any chipset register alterations you want to test (e.g. with WPCRedit), run Sandra. That's your score. I also find that repeating some tests improves performance but I believe that the fresh boot score is the true test. You never know whether some info is being cached in subsequent runs, artificially inflating your score. I find this with 3DMark 2000 as well.