Most of the 8 gauge shells I've seen in the UK were loaded with 2 1/2 ounces. That's in part due to the length of the available #8 Industrial cases that most people load in. That's about all the shot you can get in them according to the guys I know. If longer cases were available then I'd imagine there would be guys loading them heavier if they thought their guns would handle it.

DLH

Out there at the crossroads molding the devil's bullets. - Tom Waits