Stating 6.5 penetrates better is a true statement in general. We are gun people here, I assumed people could infer the context of the statement. No a 90 amax isn't going to out penetrate 220 SMK. The quick and skinny. The heavy for caliber 6.5 bullets have higher sectional density and will be going faster from the same class of cartridge, they will penetrate deeper and have less recoil, same goes for 7mm.
A 140 class 6.5 is longer than most of the 180-200g .308 bullets. Most 180-190 class 7mm bullets are way longer than 140 6.5. Elk are kind of big and not really that hard to kill. I have seen lots of them killed with a 243, with one shot. Show up with something you can shoot that has at least .243 bullet diameter to be legal for CO big game hunting. Talk to your guide, some of them do have caliber requirements. There are some that would let hunt with a 308 Win and not a 6.5 Creed how ever stupid that may be. Get some steep angle shooting practice if you can.
I think you probably need a 338/378 Weatherby, or maybe a 458 Lott. Can you find a 600 Nitro Expresss double gun? Big money east coasters usually show up with some shit like they are going to Africa to shoot a little ole Elk.
I am just messing with you, but "you's guys" do have kind of a reputation.