I run with an incredibly skilled full i90 BLM and my tank currently sits around i70. I assure you that if you don't flash 50 times there's no chance you're gonna hold hate.

I generally run into a group of mobs and flash them to death, using riot blade to recover MP in between the later casts of flash etc ~300MP and I never manage to loose hate even when he's pumping out 1600+ Dps in WP