Your previous posts in this thread make no mention of the pressures your loads might develop BECAUSE YOU HAVE PROVIDED ABSOLUTELY NO DATA. I take that to mean that you haven't collected any, and suggest you go do so before you start advising people to play with loads that are not in books. Or at very least, start suggesting to people how your DOE is going to control for tolerances in chamber size and brass thickness, lot-to-lot variations in powder, the moisture content of the powder when you're weighing it, and the other various factors that might affect the safety of the loads you are developing.
As a followup to your PCC comment, Ballistics by the Inch HAS provided data on the performance of various pistol cartidges in barrels for 2-18". Based on their data, the ideal length for PCC barrels is 12-18", depending on the cartridge. So while you could mess around to get some extra velocity or load heavier bullets, current loads are probably about ideal in terms of efficiency of powder burn.
How you're going to stuff LPPs in cases cut for SPPs to study accuracy I don't know, but there are published studies on accuracy based on primer size and flash hole size for target cartridges. There's also at least one study I know if comparing brisance of regular and magnum primers. Likely, the effects of magnum vs regular primers on accuracy are small and firearm/chamber/component lot dependent in most cases, so unless you're going to go out and collect a representative sample, the data (which you'll hypothetically provide at some unknowable future date) will be anecdotal in nature.