Personally, I'd stick with the slugs. It's hard to imagine that a load of buckshot at 20 yards will do more damage than a solid hit from a slug at the same range. I've seen deer run an awfully long way with a few pellets of buckshot in them. Sure, they can be wounded with a slug, but the chance of doing so seems less, given that there's only the one projectile.
Never have needed a scope, because I don't take shots with a shotgun at ranges more than about forty yards. Just my ethic, only applies to me, not saying you should do likewise. I hate tracking wounded deer, who don't seem to deserve the extra pain. I know--it's kinda sappy, but that's how I feel.
Best,
Jeff23