Placement is key, shoot what flys well, I used to shoot light 4mm arrows for elk, 390-420gr at about 315fps. The only fixed heads I could get to fly well out to 80 yards were solid legend and kudu 100’s, the solids flew better.
These worked excellent on deer and elk, Oregon switched to allow mechanical heads and I wanted to try them so I switched to a heavier arrow. I’m shooting mechanicals now with 500gr arrows right at 280fps. They work just as well but fly better at long distances and leave better blood trails which is important to me because I’m color blind.
I often contemplate going to a lighter arrow, if I continue to blow through elk with mine I may slowly back my weight down until I feel like I am at a happy medium. I don’t see any sense in wasting energy in the dirt behind an animal, I’ll take the added trajectory or larger cut any day. I have been staying around 280fps because I’ve always hunted ID too which required fixed heads and they are easier to deal with under 280fps. Now that ID is going to allow mechanicals I will most likely adjust my weight to allow for a little more speed.
I’ve killed elk with a pass through with a 27” draw, 60lbs, shuttle T lock at 58 yards with a 330gr carbon tech cheetah. I’ve also lost elk shooting them under 20 yards by hitting them square in the shoulder where no arrow would pass through even with heavy arrows and fixed heads.
I try to let my experience and results decide for me and help tune my setup. Currently I’m shooting 73lbs, 28” draw, 500gr RIP TKO’s with IW 100gr inserts and 25gr collars and 100gr dead meat or Trypans. They are wicked on anything they hit but my 3D scores have went down since going 500gr which means I’m less accurate. I still have over a dozen good arrows so I will shoot these until they are used up and then go slightly lighter, I also deer and antelope hunt with the same bow so I’d like to be more confident in estimating yardage.
My point is almost anything will work if your confident and hitting the right spot, IMO holding tight to the shoulder on and elk it is only a matter of time before you hit bone and lose and animism. They have huge lungs and are giant animals, I hold 3” behind the shoulder center mass and have had great luck. My kids are shooting 40lb, 25” draw with 440gr arrows and 50lbs, 29” draw with 430gr arrows for elk, both with COC fixed heads.
My advice would be to use what you are shooting. Hunting season is close and even though you can resight easily for heavy arrow your mind takes a while to learn trajectory. If your really worried about penetration ditch the G5s and go to a kudu point or similar for this season.