Had to take a proficiency test before I can hunt in the city where I live. I was using my crossbow. The shop owner made mention about it I said I hated them. Told him they were too loud and didn't penetrate worth a hoot. The last 3 years has been better but still don't like them. He told me it was because I was shooting too heavy of an arrow. I have progressively been going heavier over the last 3 years and getting better penetration and the crossbow no longer sounds like a 22 going off. I can't believe the misplaced emphasis put on speed. I feel the traditional archers have been less deceived by the big archery companies than most archers. Twenty years ago archers shot threw most all their deer that seems to be a rare occurrence today. Keep you heads sharp and may your arrow find its mark
penetration has never been a problem for me but I have never used a cross bow. for years I shot fairly light arrows (370 grains) at fairly high speeds, 290-320 fps with several different heads, these days I shoot VAP armour piercing small diameter arrows in the 400 grain range @ 305 fps and Swacker heads, they are hard to stop unless they hit bone. I really cant remember an arrow staying in a deer in the last 20 years that didn't hit the off side shoulder and I have killed a bunch.
The lighter faster slower heavier debate has went on for years but honestly I have never had a problem with penetration in 42 years of bowhunting. a good bit of that time was with a recurve and cut on contact heads and lots of different compounds and arrow/head combos BUT I always shoot fairly high poundages with a 30" draw.
I've killed a ton of deer with crossbows. If you have issues with penetration, stick with fixed blade heads, smaller diameter. If you're using expandables, rear deploying are better than the jack-knife style. Also, more arrow weight isn't a bad thing. Haven't had any issues with penetration for a while. They are loud. I've employed limbsavers AND the manufacturer's sound suppression kit. Still not great. Better than it was.
Conventional thinking today is that speed is the only way to go. Amazing that any of us was ever able to kill a deer with archery equipment before we were able to shoot 300 fps. I guess the indians just got lucky. A lot. LOL
Arrow weight = better retained energy. Usually means better penetration (broadhead design makes some difference). I'll take a little extra weight over an extra 10 - 20 fps...