I agree that turkeys are tough to penetrate, because of the feathers and feather quills, but also because they are light enough to move a little with the arrow on impact, which further reduces penetration. they don't do this intentionally, of course, it's just that when the arrow hits them, it tends to push them a bit as it penetrates. I've shot them with 2-blade, 3-blade and 4-blade heads and now use mostly Woodsman's and Snuffers. I use the same set up I use for deer. Bows in the 45# range and arrows about 500 to 525. I'd say about one out of five have been pass throughs.
(I'll add that a pass through to me is an arrow that goes completely through the bird and exits the off side. I don't count it a pass through if the broadhead is protruding from the off side, but the arrow is still in the critter. )