Finally got it over 30mh. From uber 3.1 strap, I had to bump up trc, trfc, ras2ras, and clocks now 1185/2125, running stable. Seems like the 580's need a bit more core clock, but they do take a better undervolt, so power remains about the same.
Based on what I see here, the 16.60 drivers still outperform the 17.10s, although the gap has narrowed, probably because my timings are looser than uber 3.1
AMD 17.10.2 drivers
Screen #0
ETH - Total Speed: 29.985 Mh/s, Total Shares: 16, Rejected: 0, Time: 00:08
Screen #1
ETH - Total Speed: 30.160 Mh/s, Total Shares: 23, Rejected: 0, Time: 00:08
Screen #2
ETH - Total Speed: 30.031 Mh/s, Total Shares: 21, Rejected: 0, Time: 00:08
Screen #3
ETH - Total Speed: 30.057 Mh/s, Total Shares: 17, Rejected: 0, Time: 00:08
Screen #4
ETH - Total Speed: 30.100 Mh/s, Total Shares: 19, Rejected: 0, Time: 00:08
AMD 16.60 drivers
Screen #0
ETH - Total Speed: 30.148 Mh/s, Total Shares: 15, Rejected: 0, Time: 00:07
Screen #1
ETH - Total Speed: 30.368 Mh/s, Total Shares: 17, Rejected: 0, Time: 00:07
Screen #2
ETH - Total Speed: 30.223 Mh/s, Total Shares: 14, Rejected: 0, Time: 00:07
Screen #3
ETH - Total Speed: 30.224 Mh/s, Total Shares: 18, Rejected: 0, Time: 00:07
Screen #4
ETH - Total Speed: 30.219 Mh/s, Total Shares: 18, Rejected: 0, Time: 00:07