In the best case scenarios I've seen, a "HT" core is worth half of a real one. So in these cases, a quad core with HT has about the equivalent power as a 6 core without HT. Cinebench shows some improvement but I don't experiment with that much. Last time I tried it on my main system to get a HT on/off baseline set the CPU test scored 31% higher with HT on and no other changes. Other cases I've seen a 50% improvement is a long disappeared distributed computing project called LifeMapper. Sieve tasks on prime finding projects also show a big boost but I don't think it was the full 50%.
I haven't done 1st hand testing, but I believe in some cases where people used i3 processors in gaming boxes, leaving HT on was able to show an improvement in gaming performance presumably as 2 cores without was CPU limiting, and any boost helped. But this didn't seem to help with quads (for now).
Where I've seen a performance decrease from HT is in compute tasks that do not benefit from HT at all. HT uses spare parts of the core to handle more, but some tasks already utilise the processor to the max there is nothing for HT to give, except additional management overhead and thus a small decrease in performance. Windows scheduling doesn't help either, if I run 4 tasks with HT on, you can see them wander around all 8 processor threads, and I think they're tripping over themselves for typical 10% drop in performance. If I either set affinity so they only run on one thread per physical core, or turn off HT altogether, that 10% loss goes away.
Dont get the most expensive motherboard on the market, downgrade it a bit so you can buy better or more stuff. If you downgrade your motherboard to a 100$ you could upgrade your Graphics card to probably a 980 ti
If it has to be on AM3+ (because you already own a high end AM3+ board), then FX8320, they're basically the same cpu, so the cheaper one is the better one.
your rig would pull around ~500W when under gaming load, so the AX860i would be more efficient
also, its best to get a smaller wattage psu due to efficiency during idle
and some PSU shuts down if the wattage is too low (but i doubt this will happen to these psu but meh)