I'm looking at some Centerline Grizzley's I really like in 16X8, but they have 0 offset, meaning 4.5" backspace.

I've heard that running less than 4.5" of backspacing is really hard on wheel bearings, etc. and that 5" is better for a stock height truck.

Since there's very few wheels out there with 5" of backspacing that are 16X8 with 8 lugs on a 6.5" circle, what do you guys think?

Is 4.5" of backspace just enough?

I wouldn't worry about it too much, your wheel is going to be 1 1/2" wider than stock and have a 1/2" less backspacing so it'll stick out two inches more than what you have stock. You wheel bearings might go out a little sooner but I wouldn't worry about it too much.