With decent water cooling you can go WAY over what MSI AB lets you set the sliders too.
This was for the thief benchmark thread. Oddly enough, i was being held back by my CPU and its clock! People with similar clocks on 290x with 2011 socket CPUs seem to be benching higher even on mantle!
Here is a link to the guide if you want to go over +100mv i would be surprised if the lightning couldn't handle +200mv for a bench or at least +150mv for 24/7. How hot are you guys getting on your lightnings? Previous lightning coolers could handle as much as some AIO set ups and ive seen previous lightnings eat up +200mv no probs. Maybe some extra case airflow could make it cool enough to run higher than +100mv for you guys.
http://forums.overclockers.co.uk/showthread.php?t=18556274&page=2
My screenshots above were on a reference card with an EK block and before i dropped voltage down to +231, i had it at +275mv without issue when i was playing with higher clocks.