RE: What broadheads for turkeys???
 

NAP has a special made broadhead for turkeys called Gobbler Getters, its been on the market for a few yrs now. I've used the head, and have had excellent results. I nailed 2 turkeys this fall with my bow. The arrow stayed right in the bird both times, and prevented flyoff. This was w/o cranking my bow down from my deer hunting weight.
Its best if you can use a broadhead that'll actually slow penetration, and keep the arrow in the bird. This prevents the turkey from flying off after the hit, keeping them on the ground for recovery. If the arrow passes through the bird it may fly off. Unless you can see him fly across a field chances of recovery are tough. The NAP heads are basically a spitfire with a blunt tip.

RE: What broadheads for turkeys???
 

Though I also agree keeping the arrow in the bird
is best...it is by no means a guarantee. In the last
4 years I've had 2 gobblers fly off with my
arrow. Each time, after rolling the bird and believing
I had made a good hit, each bird jumped up and
flew away when it saw me leaving my blind. After
seeing this happen not once, but twice, I now aim
at the top of the leg/bottom of the wing. This prevents
running and flying, most importantly, recovery of
the bird.

CW, 50 lbs. is plenty for turkeys. Thunderheads with
a adder point or other arrow stopper would be fine.
If you go with a mechanical, I'd recommend a cut
of 1 1/2" - 1 3/4".

Good Luck