Ahh, I think I now see why Lowell stirs the pot. Controversy seems to raise many considerations to the surface.
As for velocity loss from overboring, I would think it'd be pretty much a moot point unless the wad doesn't seal as well. There seems to have been much written about the plastic wad bases doing pretty well at sealing in larger bores. If they do indeed seal as well in a slightly larger bore, the results could very well be an increase in velocity due to larger piston area. My calc says about a 2% increase in area for .010 in a 20g. Might increase the accel for the same pressure, but pressure may drop a bit. So, I'm betting on all of it being in the scatter and essentially no change in velocity.
