It may or may not make any difference. Very application specific.

I don't think there is anything wrong with trying it 4 degrees advanced and seeing how it compares to the 2 degree advanced that you have been running. Are you sure you have enough valve to piston clearance to move the centerline? That is the only thing I'd worry about. If you have enough clearance to play with the centerline then go ahead and try it at a few different spots and see how the engine responds.