Hm, with 16Gb VRam this shoudln't quite be a problem. Look at my specs: GTX 970! It has 4Gb VRam and I run and save 3000 x 3000 fluidly and without any troubles. Turning off High Quality will actually make this run as smooth and fast as it can possibly go. I'm a little surprised right now myself, haha...I hardly paint at such resolutions. At least not for fun.
...but, yeah, maybe I should?! Seems like a clever idea just to stay on top of things, regarding potential troubles.
But, yeah, so 3k is no problem.
Try turning off High Quality and see, if that makes it more stable for you?! The other minor wildcard is win10, though, I have tested it on it successfully with an Intel HD4400, I think, some intel card. I'm not sure what to tell you, you know. Strange.
When I get to enough money again, I will invest in different systems for proper testing. I hate to mention this, but it's the truth and I want you to know that I care and can't wait to address such things directly. Right now I still have to fly blindly, making assumptions about what could've gone wrong on AMD. However, I could at least release a "log" mode, which may help to figure out at least where it breaks down.
Alone the idea that it "just closes" suggests that there's a GL problem, that's for sure. It means that it wasn't an "access violation", but some other collapse of sorts that the OS never got to know (hence on graphics card). At least I think so.
Anyway, thanks once more for helping me look for it. At least you made me try out 3k again and I might make a big doodle just to run it through its paces there.