Debates such as what's been mentioned will go on forever. Fixed vs Mech, light vs heavy arrows, FOC, etc... The bottom line is, understanding your equipment's limitations as well as your own personal and then being disciplined enough to stay within those limits. In order to be effective at killing an elk the arrow must have enough Kinetic energy to penetrate into the vitals from whatever angle you're shooting the animal at. Unless you get real lucky and hit a main artery you need to take out the heart, lungs, liver, diaphragm, or any combination. Quickest is heart or double lungs. Single lung, good luck. Hit liver only and you have a long waiting game.
Some people prefer a heavy arrow set-up such as 500+, that's totally fine, however, unless your shoot an 80lb bow your sacrificing a lot of speed with those heavy arrows.
I feel there's a balance to be struck between speed and arrow weight. Obviously the faster the bow shoots the flatter the trajectory which results in a larger margin of error in judging yardage. 5 yards can make a big difference when you're shooting out to 50-60 yards with a slower trajectory. You can't always get a range on an animal unless your absolutely disciplined enough to say you're never going to shoot at an animal unless you've verified the range.
Over the past few years I messed around with arrow weight a bit. I used to shoot a 438gr arrow, I then went to a 453gr arrow, and my current set-up is at 478gr. It has been interesting to see the difference in my pin gaps, I shoot a 5 pin slider. With my current set-up my pins are spaced from 20 to 60 yards with very little difference in the gapping. With my previous set-up at 438gr the pins between 20 & 30 were very tight, from there the gaps began to get larger between distances out to 60. This is a function of lost energy as the arrow travels down range. So what this has told me is the heavier arrow maintains more of it's energy at longer distances. Higher energy equals more penetration. So using a set-up that provides as much Kinetic energy as possible while still keeping a balance between speed and arrow weight is where we should try to be. What is the right number to target for kinetic energy, I'm not sure, some varying opinions on this. There are several places online such as arrow manufactures that provide a kinetic energy calculator. Kinetic energy is a function of arrow weight and speed.
I feel the type of broadhead you want to shoot plays a factor on what your total arrow weight should be. I will say this if you're going to shoot a mechanical or hybrid style broadhead at elk, my opinion is you should absolutely have a set-up that leans to the higher side for kinetic energy, I'm thinking somewhere in the 75ft/lbs plus but a part of that equation is a heavier arrow to maintain the energy downrange, unless you restrict yourself to very close shots, heavier being in the 450+gr.
My current set-up is 70#, 478gr, 29" arrow, speed 272, 78ft/lbs, 125gr Evolution Hyde broadhead.
I shot a bull this year at 50 yards. The bull was slightly quartered away. Arrow entered on an angle near the back of the ribs, took out both lungs and was poking the skin outward on the opposite side just behind the shoulder but did not poke thru the hide. Massive wound channel. Elk went 100ish yards.
I've shot many other elk with varying combinations of arrow weight. All my set-ups have shot over 270fps. In my younger days I used a light arrow, I'm talking 390gr because I like the speed I was getting, however, I quickly learned that I was sacrificing penetration, so I went back to a 438gr arrow and immediately had far greater results.
These are my opinions based off my 36 years of archery elk hunting so take it for what it's worth.
