you were planning on shooting an elk with a rage with a 50 lb bow and 27 inch draw? i suggest some kind of single bevel broadhead that will give you way better penetration than a mechanical with your poundage and draw length.
for arrow shaft the heavier axis would probably best for you to get your momentum up. as for size i ran your setup on the ot2 app (rly great for android for messing around with potential arrow setups), if you shoot the standard insert with a 100 grain head and easton axis 500 cut to 26.5 and shooting your nitrum 30 at 26.5 and 50lbs would be a perfect spine match. it says numbers will be around 246 fps ke 46 foc 14.6 mo .378
or you could go way heavier, slower but with more ke and momentum and punch.
you would need your bow at 27 50#. would be a 400 spine easton axis with 125 grain broadhead, cut to 28 inches, 75 grain HIT brass weight, you have to shoot all that weight up front otherwise you will be too stiff. brass hit weights are around an extra 20$ on ebay) numbers around 219 fps ke 50 mo .455 19.49 foc
in my opinion if i was in your shoes i would shoot the second one for big game. heavier arrow will be quieter too. forget about the speed. quieter is better. an extra 25 fps wouldnt beat the speed of sound. id be interested with what others think but screw a 125 single bevel head and i think you will be good to go. downside would be you wont shoot as flat but just practice a lot and practice judging yardage. hope that helps