metro,
Anyone who knows me knows I'm always advocating to error on the heavy side as far as arrow mass is concerned.A heavier arrow always delivers more "punch"but in your case imo you've got a lot of"punch"to spare. To put it in perspective I took your conditions and scaled it down to 55 pounds peak weight but increased the arrow mass to 600 grains. The new calculated values are 65.2 ft/lbs ke and 0.59 pound seconds of momentum. Almost everyone would agree that 55# and a 600 grain arrow launched with 65.2 foot pounds of ke (that's221 ft/sec)is more than adequate for any elk or even moose. Now if that is adequate, your setup outperforms this one both in ke and momentum right on out past 50 yards. So in other words you are delivering more "punch" by any measure be it ke or momentum than the same bow set up at 55 pounds peak shooting a 600 grain arrow at virtually any practical hunting distance. Anyone who agrees that 55# peak and 600 grain arrow will do the job can't argue about your setup even with the 347 grain arrow.

I hope this little exercise helps...