The RX 480, 580 and 590 I seem to begin throttling on some cards in the upper 70's. It is a bit of the silicon lottery here as some are fine heating up to the 90's while others seem to have issues in the high 70's. Raise your fan curve to 100 percent at 70. If that eliminates stuttering then you were probably experiencing thermal throttling.
This website lists most CPU and GPU Maximum Operating Temperatures. The RX 590 is too new so it is not listed but the RX 580 is list which should be fairly close to the RX 590 or the same:
I new someone would post that! I'd say thanks but it's listing is crap as most if not all 580's throttle way before close to those temps. It may be a max temp on paper only just before the chip explodes. As I already said you will throttle at those temp making the card very unstable causing at minimum stuttering at maximum crashes. Do yourself a favor and try try to keep your temps in the 70's.
I can't vouch for the info in the website image I posted. But they seem to be fairly accurate. Most of the time I have checked, at least, the CPUs and they are in agreement. GPUs are difficult to locate Max. Operating Temperatures since most of the time it isn't posted. So I use this website as a general rule.
For instance, here is what it says about my GTX 1070:
This website seems to agree with both of us : https://www.wepc.com/tips/optimal-cpu-gpu-temperature-gaming/
thanks all. its to a max of 83 c so far.. it has yet to throttle back. not even sure how to cool my pc down anymore then it already is with all fans running at max. i am getting a new cpu fan soon. not that it has any ability to cool my gpu any.
My point was not that it is not accurate by the white paper that AMD publishes. It's just that many of the 580's don't do well at what is supposed to be acceptable range. That is my point. I like let people know that is not abnormal so they don't go buying more fans ad power supplies thinking that it other issues causing throttling. The 590 are on a die shrink and should do better. There are several reports here in these forums however of them still throttling in the upper 70's.
You could ask on the card maker(xfx, asus, etc...) support/forum if you need a definitive answer.