i like the heavier bhs , the heavier foc, and fpe , but these excals are powerfull enough to punch thru about anything even with lighter heads, it will beccom a matter of preference
The Firebolt with a 125gr head weighs about 390 gr.
The Phoenix advertises 305fps for a 350 gr arrow
Subtract 1 fps for every 5 grains of weight , means you should be shooting a 390 gr arrow about 297fps. That equals about 76 ft-lbs of energy at 0 yds.
This setup should be around 279 fps at 30 yards = 67 ft-lbs
A FB with a 150 gr head = 415 grains.
Initial velocity = approx. 292 fps = 78 ft-lbs of energy
At 30 yards that setup will be moving around 275 fps = 69 ft-lbs of energy
A lighter arrow slows down faster than a heavier one and sheds energy faster. But a lighter arrow shoots a flatter trajectory than a heavier one.
A heavier BH will give you more FOC, which will help stabilize the arrow quicker. Higher FOC helps penetration too.
Using fixed blade broadheads will up your chances for a pass through IMHO.
I use roughly a 415gr setup for deer, and go up from there for bigger game. I am going on a bison hunt and my setup for that right now is about 535 grains.
All of this ends up as personal preference.
Good luck and good hunting
Keith
Stand by the roads and look, and ask for the ancient paths; where the good way is,
and walk in it and find rest for your souls. - Jer 6:16