Since you're a resident and can go up in the wilderness area without a guide if you have to because you see a few more people than you like down lower and you're talking the last half of September on an archery permit I'd say go in a heartbeat. For what you're talking about I don't think you could go wrong on an archery tag that time of the year. I would probably not recommend either one for rifle season with the large number of people that go in those units then. I hunt the west side of the BigHorns and have every year for deer and/or elk every year and have since 1994. The entire mountain chain is on the upswing for elk numbers and if I were you I'd buy the tag, an archery permit, and take the whole two weeks up there if you can swing it.