There is only one socket that's currently NOT dead and thats lga1151. Even lga1150 is a dead socket, same as am3+, so that 'it's a dead socket' argument doesn't hold any water whatsoever. My Lga1155 pc's are well dead too but I'll be damned if a 3570k and a 3770k can't hold their own against anything newer. Fact is, most ppl do not upgrade just a cpu, they'll either upgrade the gpu/psu or start a new build entirely. And to top that, Lga1155 boards / cpus are no longer mainstream production, whereas AM3+ still is. With an Fx 8320, there honestly IS no upgrade, the 8350,8370,9370,9590 are the same cpu. Would be no different than pairing a 6700k on an lga1151 board, there is no upgrade, so even an open socket vrs dead socket doesn't mean jack s.. t.
An OC 8320 with a r9 390 will perform in real no different to a i7 4790k with a r9 390 at 1080p 60Hz. The framerates will be so far over 60 with either cpu that only benchmarks will have any bearing, which is to say exactly none. To a 60Hz monitor, it makes exactly no difference if the 8320 only manages 120fps to a 4790k's 200fps. Both get capped at 60fps.
Either way, Op needs to drop the psu for a less expensive, but definitely better psu and apply the money towards either a better case or a 120/128Gb SSD if performance in and out of games is wanted.