I've used both Steelforce Phatheads and Stingers on Whitetails. It's a coin toss for deer. Both brought passthru's and quick kills.
It going after elk, the thickness of the Phathead is 2nd to none.
If your plan is to go out and purchase some heads because you own neither, then I'd suggest the Phatheads.
Nick from Steelforce says the Phathead is the head he suggests for African big game. A hunter using a Phathead got a complete passthru on a giraffe, which is next to unheard of. If you can get a passthru on a giraffe, with super thick leather hides and a body like a VW Bug, I think it'd zip thru an elk.