I was just thinking about this the other day. It's really a matter of arrow weight and speed, not poundage. Especially with some of the super fast recurves out there now. Also, a long draw will give you more fudge factor. I don't have an experience based answer for you on minimums, but I would think a well tuned 550 grain arrow at 150-160 fps and a two blade broadhead is enough for elk.
Personally, I'd really rather have an extra 15 fps out of that 550 grain arrow and would use a high quality 4 blade, like an Iron Will if I were chasing elk. I'd expect a passthrough with that setup if only hitting ribs. But all my elk killing experience has been with heavy longbows, 2" wide Simmons sharks, and 750 grain arrows, so take this with the proverbial grain of salt