RE: Too fast for broadhead?
with a great tuned bow no problem! if you can tune really well you can just about get any head to fly good. I would suggest a simple of things that might make your life easier at those speeds.
1. use feathers
2. use helical
3. use the best carbons you can buy (straightness goes a long way!)
4. make sure your inserts are straight & the heads do not wobble.