Haven't really tweaked much, but a simple 50x Multi on all cores pushes the vCore to 1.372v on AUTO, which I think is pretty neat and for an auto setting rather accurate. Its not AVX stable then though, and core temps spike to 92-95C (only briefly) and stabilize at 85-90C with AVX. A tad too high for my liking.
I kinda predicted for myself that with this setup/cooler I would be able to handle 1.35v and that seems perfectly accurate, when I put an offset to hit that voltage, I get 1.344v in AVX and I can push 4.8 on all cores stable. 4.9 bluescreened on me with OCCT Linpack. Temps spiked to 90C (only once) and stabilize at 80-85C. Its on the edge for my tastes, but I never use 12t AVX loads, so I've already settled for 1.35v and I'm going to play within that budget. There's a lot of a smaller voltage tweaks to be had, and I may even just disable HT until I find a workload that really benefits from it, and chase that 5.0 GHz again
For non-AVX stress testing (OCCT regular, 15min run) I'm looking at 60-75C tops on this cooler @ 1.35-1.36v which is pretty awesome for a heatsink and two fans IMO.
Gotta say as well that this K6 is a REALLY nice board. Good UEFI, everything works well, but of course, the software tweaker in Windows (F-Stream) is a steaming pile of crap
Already crashed on me several times, and GOD is it slow and heavy. After my little OC adventures I touched the VRM/heatsinks: lukewarm at best. This board could probably sustain 1.5v easy and fry that CPU.
As for the CPU, its not a dud, its not a golden ticket either. I can live with that ^^
Thing I'm most in love with right now though is that case. So compact for ATX, its brilliant.