For speed runs, I normally run with a premade. If I DF on my PLD, I check to see the gear of the group and class composition. If conditions appear to be good I'll attempt a speed run (and if not, I opt for a normal run). If it looks like the healer is struggling, I slow it down (or if someone asks to slow down). If I DF as my BLM, I let the tank set the pace just because that's the polite thing to do.

I don't like pushy DPS or healers. And no one should be expecting speed runs in a DF group to begin with. More often than not, the DF pugs I come across are geared just enough for the dungeon and not for much more than that (there are exceptions, ofc). And to expect them to do speed runs is ridiculous. I do firmly believe that if you want a speed run you should make a pre-made group.