There you go! H98 will take over from here on out. I think you've found a good place. Basically, your card was throttling at your previous 1415 speeds. That's why your minimum FPS was poor prior. That means your card was seldom hitting 1415 during load. Power Limit just means throttle limit. When you max that out, you're allowing the card to freely draw the to maximum designed limit. What I can't understand is if it's the 185TDP "rated" limit, or if it's the 225w connector limit. Either way, maxing out the power limit of the RX 580 seems safe and a must (AMD's indirect advice) in a Mac Pro since both are at, or under, 225w. More confirmation is needed, but I'm a conservative person, and I'm convinced. The cards come stock, especially the refereced card, with power savings turned on.
So you win. I will say that I paid only $300 shipped/after tax for my card.
Maybe, if I find some kind of hunch, I'll start raising my voltage and overclock to the MSI Gaming X figure. Believe me- the reference blower is pretty good, and I have a lot more headroom. But another 3 FPS with more noise, thermal, and heat, doesn't seem to be a worthy proposition with a blower cooler.
btw, in Watmann, bring the prior states to 1075mV if you find any states that are higher than that. That's a simple, easy way to do it. In other words, states 3-7 should ALL be 1075m or lower.
When you FLASH the card, H98 will talk you through. Flashing requires more testing. More than what Heaven 4.0 has to offer. You probably should run a few rounds of Furmark at those settings. If it's safe, then it's flashable at those settings.
The big point is, is that the RX580 "out of the box" is pretty unsatisfactory. Poor optimization. +/- 3-4 FPS in a given benchmark at 1440p is not acceptable. My 1440p benches ranged from 41AVG FPS to 45FPS. When I unvolted it, raised the power limit, it's 47.6FPS every. single. time. now. 41 FPS vs 47.6 @ 1440 is absolutely significant.
Yep, it's time to fall in love with the RX 580!