With Stoneskin, Megaflare can't kill you with B4B on. Gear dependent I suppose but I think as long as you have some i120s/i130s left-side you should be fine and can use it without abandon in your opener.

I actually DGAF about B4B in most of T13 as DRG with a decent amount of i130s. Basically the only thing that scares me is final phase Megaflare > tower/nail/whatever explosion, I won't B4B before Megaflares there, not worth the risk.