no worries, the bios should be quite easy to guide you through, keep testing the ram and if it passes then thats a good sign, my next move is the bios and if that still doesn't work, your gpu will need looking at, have you got a friend who could lend your their gpu to test? (that will be if the bios doesn't sort the issue)
if your ram is running 1600mhz then its set up correctly it will be running at 3200mhz (ddr =double data rate).
i'd say next thing to try is another gpu, ask your friends if they'd be kind enough to lend you one for testing, if not head on to the b-grade section of overclockers and pick up a card, £100 mark should work for testing, don't go all out and buy a new one as the problem could be elsewhere.
i'd say its something between the gpu or the psu, but hwmoniter showed excellent voltage readings for your psu so i recon its your card, but testing another is the only way to be sure.
but going back running all the stress tests should have showed problems as they are the worst case for a pc, and all passed.
The games your having problems with, did they get any updates lately? or are they in alpha phase (pre release?) could be a update has knackered the game or the alpha release has got bugs in it unbeknown to the developer
i know it will be annoying but all the symptoms are pointing to the card, you've tested the cpu, ram all came back solid as a rock, plus your psu voltages are all excellent, yes I'll give you that the pc passed a gpu stress test which is odd but gaming puts far less load on you components. as to why its not working properly it's an interesting one for sure but for me it's pointing to the gpu.
when you fist built the pc was everything running perfect, able to game surf the web and no issues at all?
final thing to try is reinstall the affected games but not fully update them, if the crashing goes away then its software (game) related, but if the issues still persist after re installing your games it time to look at your gpu unfortunatly