The voltage seems to be high for that clockspeed. The HT link should be kept close to 2ghz, as well as the NB. Increasing the NB yields a benefit in benchmarks and synthetic metrics. Increasing the HT does not, and it is generally acceptable to keep it near stock.
I believe the 620 is 2.6ghz (13x CPU multiplyer). I would probably start with a 250FSB (3.25ghz on the CPU), x4.00 memory if it is 1066ddr2, x8 HT (or 1.6ghz if bios reads it that way) and x8 NB. I would bump the memory volts to match 1066 requirements, and probably put my first try for the CPU at around 1.425v in the bios. If it didn't boot, I would bump the CPU volts until it does.
If this is stock HSF, I would probably even drop the cpu multi to x12.5 or x12, though many claim that the stock cooling is good to 3.5ghz, I am more cautious about heat. 1.488v has to be creating a lot of heat on the CPU if it is stock HSF. Though, the Athlon IIs do appear to run rather cool compared to the Phenom IIs I have primary experience with, probably due to the lack of L3 cache, so whatever you can tell us about your thermal situation might help get more advice.