Here are my thoughts--keep in mind I train for this year-round and I take the least/smallest/lightest gear (my bivy hunting pack, full for 6 days, is around 25 lbs). I've packed 1/4's to 1/2's of bulls up to 8+ miles, and can manage to fit 1/3 of a bull in my pack along with camp.
Don't shoot an elk over 3 miles away if you plan on packing it out yourself.
And if the terrain is ugly (which it should be if you want to find elk!) cut that distance in half. It's very easy when bivy hunting to work your way 10-15 miles back over a day or 2 of hunting and moving--be mindful of this. Last year's bull was 12 rough miles from the truck, and we got no cell service to call a packer. My buddy and I spent 2.5 days packing it 6 miles to get to the nearest trail, then ran into town empty and got a packer. The meat would have spoiled in another day or 2; it was stupid on my part to shoot him without further plans, but we made it work. I don't suggest that strategy, ha.
Best of luck!
Pete