Bclk got worse at lower temps as well as higher multis. Was able to boot at least 400 bclk at -100c and lower multi. Not sure if cpu is core limited or limited by the combination of temps, bclk, and multipliers that are possible. If anyone knows how to force single core boost to all cores please let me know, should help me narrow down what's holding me back. msrtweaker doesn't work at all and k10stat didn't seem to do anything useful