I know the OP pain as ( or so i thought at the time ) my 780 was a terrible OCer, i could not even get 80+ on Core without a driver crash but this is where it gets interesting for me anyway. I was tinkering with my CPU OC and remembered i had a TPU switch on MB for OCing so i turned switch on and noticed my CPU OC was way more stable and could even go higher. So for fun i cranked up OC on gpu up to 80 again and ran Heaven and no crash this time....was like hmm..played crysis 2 for little which always pretty much showed me weather my OC was stable or not in mins. So then i went 100+ on core, tested again and same results, no crash. So then im like yolo! Cranked it up to 150 on the core and still no crash, was like what the....added 60 to memory and still stable. 
 
Now as far as i knew the TPU switch only effected the CPU for Ocing unless it somehow effects the power output on my MB and allows more juice or something idk...ill be honest..i have not googled as i did not want to know lol, it worked so wasnt complaining at time but the total boost clock of that 780 went to 1203 total with 160+ so def was not bad.
 
 
I found this out after i had my 980 ACX that i sold and the acx i had seemed like a bad OCer also, barely 1400 but wish i had tried the TPU with it to see if it mattered or not, who knows maybe it dont but the 980 classy i got now OCs way better, 1542 total with 100+ on core and mem and no voltage or power target increases yet and while gaming the card aint even at max usage at 1542 which makes me think i can go even higher but staying at 1542 for now. 

rstaniforth
What benchmark software do you use?
I'm finding Valley is probably the one that I get the least crashes from so I'm sticking with that, but once I find a stable clock (if I can get higher than before) then I'll put it through the others and some FarCry4 game play.
 
Well, you say that, I've got a slightly annoying and getting worse coil whine on my GPU at the moment so I'm considering sending it back anyway, but I'm not really one to moan about things like that.

 
I use Heaven and uh, ( just reinstalled windows so not sure of settings ) i use extreme, ultra, 8xaa, pretty much everything max except tesselation and use ur resolution ur monitor is. 
 
And depending where u got the card from say like newegg, u can might even send it back in and exchange it, specially if it has coil whine u have ur reason right there and specially if its that bad of a OCer. Some ppl say its lottery and just deal with it but the money ppl put on out these cards, they expect good OC results so i would have 0 issues RMAing the card and saying hey i want a exchange where ever u bought it from.