I'd recommend being very cautious when increasing voltage with V9, given the increased power use from spikes.

Same settings V8 vs V9 on my Fury Nitro (1140/550, -12mv), GPU CORE POWER:

V8: AVG 207W; MAX 274W

V9: AVG 210W; MAX 370W

Only a 3W difference in AVG, but a nearly 100W change in MAX. Big difference to begin with, and enormous in an multi-gpu setup.

(As it stands, undervolting to -96mv and reducing clock to 1110mhz saves me 40W on average V9 vs V8, but the MAX is higher in V9 even when significantly undervolting from V8 (283W vs 280W))