If we are talking about plastic wads and plastic hulls, changing the pressure by 1500-2000# is a lot, and there has to be a significant variable going in (amount of powder/shot or type of powder) or coming out (velocity or payload). Offhandedly, I can't recall seeing a list of ballistically similar recipes that can generate that amount of change merely by substituting a wad.
Each gauge has a sweet pressure spot for performance, and it is typically at the high end. That said, I typically load my shells a bit on the light side and use clone wads. The loads go "bang" every time, don't kick too badly, and targets break. That's all I ask for.
