I7 multiplier jumpy on ASRock X58

Not sure if this is a known issue with this board (ASRock X58 Deluxe) but when I set my i7 920 to 171 bclk and x21 multiplier, the motherboard will report it as 3.59 GHz, but in CPU-Z the multiplier will jump between 20 and 21. I have tried disabling all the power-saving options and thermal throttling, but it always jumps between 21 and 20 when under about 50% load. When I take all load off the CPU, it will stay at 21, but when I start up prime95, it goes back down to 20. It runs about 47C or 34C (should I read the CPU temp or the "core" temps in speedfan?) idle and 52-55C under load.

Also, the reported voltage changes, says 1.16 under load and 1.2 idle, even though I have set it to 1.275v in the BIOS. Is this a good voltage for 3.6GHz or should it be lower/higher?