@Klee That are very interesting and in-depth observations. I do understand, that it doesn't make much sense to load one module with two threads; the shared ressources, the 2 MB L2 cache a module. But the even vs. odd thing is still very strange.
W
hereas, the mining software and/or the OS scheduler seems to play a role, as well. You observed the max hashrate at 7 threads with xmr-stak-cpu. With xmrig by contrast I got the highest hashrate with 8 threads; with 7 threads not much lower (305 vs. 297 H/s with Opteron 4284), but not the drop you observed.
But you are right: Bulldozer has an extraordinary hashrate per module. Not even the AMD Zen arch, which performs very well with Monero, has such high hashrates per core. Otherwise, Bulldozer was trimmed by AMD far above its sweetspot regarding
efficiency. To get max hashrate per watt, Bulldozer would have to be driven at much lower speed and Vcore.
If you don't have to care about
wattage and acquisition costs are your primary criterion, the Bulldozers at eBay might be an
insider tip...