305's on an 11" rim

I haven't run that size on an 11" rim, but I think you'll be fine. The recommended range for a 305/45/17 goes all the way up to 11.5", so you're fine there.

In general the tires will look better if they're on a rim that's closer to the minimum recommended. That's especially true with the larger diameter rims because you get a little bit of sidewall bulge back. But I think the taller tire will actually have a bigger effect on the look than losing a little bit of width.