Elk are tough, and there's alot of difference between the size of a cow or young bull vs a big bull. Personally I'd set my own minimum for elk (for myself) at more like 55 lbs range with a reasonably efficient bow, I like a bit more than that. I like to shoot big Snuffers though too. I've seen elk hit really well go farther than you'd think, and marginal shots/penetration are bad news in elk country. If you are an expert elk hunter, or spend months with them passing all but perfect shots I'm sure you could get away with light equipment. As a guy that's hunted them around a dozen times and killed a handful, I'm no elk expert, I'll take the medium or better weight equipment for the added margin of error, and big broadheads.
R