Absolutely they are big enough. I use 125gr muzzy or nap thunderhead myself. The key thing on a elk broadhead is the tip. It needs to be a either a fine constructed chisel point like the old bear broadhead or tips with the hollow ground point or longer three sided points. Definitely stay away from the ones that open on impact. ooohhhhhhh those are not good on elk. Rips the blades right off.

Probally the best elk broadhead going for their heavier structure is Muzzy, that longer hollow ground point allows for the point to bust a rib into before the blades come in contact with the rib. It also drives into the animal straighter than the old round pointed broadheads.