a 2 blade, COI head will give you the absolute BEST penetration qualities without a doubt - and that is proven fact
True, but I would only recommend a two blade COC broadhead in situations where penetration might be a problem due to a very low powered bow or perhaps on huge game animals where penetration was by far the main issue. Why? Because despite the excellent penetration aspect of two blade heads it has been my experience that they just do not yield that great of a blood trail. All 50lb and up compound bows being sold out there now will easily blow a 3 blade fixed head through deer sized animals. So I see no need to use a two blade head that is better suited to traditional bows or youth bows.
I do have to admit, though... I've yet to hit a shoulder to put it to the real test and I don't intend to do so intentionally.
Well hitting the shoulder on a deer is a dicey thing with any head. I won't claim that it would always go this well for me on such a shot but I put a Grim Reaper through a 230lb bucks shoulder in Illinois last year. My fault on the shot. Deer was moving and I couldn't get him to stop. Aimed a little foward to compensate and hit him exactly where I aimed. Grim Reaper blew through that shoulder and buried dead center in the bone of the offside shoulder. Buck snapped my arrow in two, ran 70 yards and died. Had to use a hammer, pliers and a chisel to get it out of the bone of the far side shoulder when we skinned the buck. Given what was hit and the size of the buck, I'm pretty sold on Grim Reapers now.