Max weight is hard to say without some details on the plane. Wing design and position can make a lot of difference. You can overpower all day long, but if you get too high a wing loading then you end up with a flying brick. With higher weight comes longer takeoffs, faster landings, and higher stall speeds. You also have to look at the higher stresses on the airframe.

I am all about overpowering planes for fun, but sometimes you have to take the bad with the good. Give us some more specifics on the plane and the engine and someone can point you in the right direction.