Disabling P2 on 5x1080ti (3 diff brands) nets me 1-2% increase in hashrate at expense of 2-3% power usage - not worth for me, especially that it matters mostly in memory intensive algorithms which, as all we know, 1080ti are lackluster with.
P0 it's a question of stability when working close to max. P2 will crash when miner exit, P0 won't.