From my experience it is not an issue of the gear it is more the skill of the player. The tank's gear will play the biggest role, but as with all its about player skill and working together.

I have pugged and done FC groups, and an FC group of just hit 50's in AF's and whites and things ran smooth, but pugs where all have run things and have better gear are horrible. Some stuff really isn't meant for the DF (if you want quick smooth runs) and this is what FC and Friends lists are for. Queueing with 2 or 3 friends (more for 8man stuff) will almost always lead to a better run then having all randoms.