I had to pump 2.8 volts through my K62 500 to get it to run at 560 (112x5). I was using a OEM P3 cooler (the one that comes in a boxed Coppermine, the larger one). It idled at around 46 C according to MBM and was about as high as I was comfortable going with it. If you've got a Millenium Glaciator or a PEP66/Delta on there, it could probably handle 3+ volts.... but seriously, if you're using this as your primary computer, this chip will fry in short order. 500 MHz out of a 400 MHz K6-2 is pretty dang good and you're hitting the max that those chips can go to, for the most part. If you really want to go after it, remove the aluminum plate on the chip (make sure to clean the glue off) and set the HSF right on the core. What motherboard are you using?
SickBoy