Personally I hold PB for high damage spike requirements. It probably works out higher to use PB at start on a dummy, but in real boss fights where you are fighting multiple targets and losing contact with boss etc, I found that you really only get to use that start mechanic maybe once and then you can end up losing all your stacks 5 secs later anyway because you have to dodge an aoe or fight mechanics. Therefore I find it more useful to save it for when you have a boost CD ready and know you'll have ample time to spam it on the mob. Garuda, Titan, ADS are all examples of this kind of fight.

I also use IR and BfB separately to boost damage through my entire rotation. I used to stack them but I think its more efficient this way. I haven't had an opportunity to test with a parser, but mathematically it should provide more advantage as monk has a more accumulative damage effect.