So my Sapphire Nitro+ RX580 Limited Edition cards came in today, so I ran some benchmarks.

I first tried to find the highest error free memory clock for each memory strap and chose one that performs the best.
I followed this up by downclocking the core until the mining performance was noticeably affected if I'd gone further.
I then proceeded to reduce voltages as much as possible.

The trials and results can be found here:
https://drive.google.com/file/d/0B0CbyDF8Rhg5LS1CdldsUGs5OTQ/view?usp=sharing

I was able to achieve 29.3Mh/s at 77.5W as reported by MSI Afterburner and HWiNFO without any reported memory errors. After 1 hour, the card remained at 42 Celsius in a 72 Fahrenheit ambient room using only 40% fan speed. If power isnt an issue, the 1450 stock clock at 1.125V which can go higher would do great for dual-mining.

http://imgur.com/DnB9WH1

I have 6 more of these to play with, and I'm looking to reproduce these results. If anyone has any custom memory straps they'd like me to test just send me a PM (these use Samsung memory).

UPDATE:

After additional strap tweaking, I've gotten to 30.5Mh/s Eth. The card can dual mine 1450 Mh/s Dcr with no power limit, however by balancing power to hashrate, I get 1130 Mh/s Dcr (w/ 30.5 Mh/s Eth) @ 125W

UPDATE2:

The Nitro+ RX580 seems perfectly happy to run on just a single 8-pin power connector. However from my tests, this reduced hashrates by 1% and power consumption by 1% consistently The 1% drop seems to only have been temporary.