I always wonder why the mechanical shooters get so defensive when guys who prefer fixed blade heads talk about penetration. I've shot mechanicals, really just because I wanted to do something different. I've used them on deer and pronghorn hunts, and turkeys too. I still wouldn't use them on elk. That said, my hunting partner shoots NAP spitfire 100s and he's killed three bulls with them, and none of them have gone far. He shoots a heavy poundage bow that is fast, and the only reason he went to mechanicals was that he couldn't get good arrow flight with his satellite fixed heads. I suggested he tune his bow better, but he chose the other route and has had good results.
I prefer to tune the heck out of my bow and get my fixed blade heads to shoot very cleanly, and to hit the same point of impact as my field points, out to at least 50 yards. If you do that, you don't need the crutch of using anything else.