The 7.62x39mm might not have the reach you're looking for in Colorado. The 557 Carbine in 30-06 might be about perfect, and I agree on iron sights. I'm waiting for the .308 version, myself, but that might be a while, *sigh*.
It amazes me how many people dismiss iron sights. I could never imagine owning a rifle without them. And before I get lectured about them on this tread, "ITS MY PERSONAL PREFERENCE!". Lol.