I am no expert at reloading, but have used the above formula for some time. I understand that 800x works best with a heavy load on top of it. When you drop the load weight too much it can result in irregular ignition.
What you talk about in theory is generally true, if you drop either the powder or the weight it usually gives a lower pressure. The devil is in the details though. You really don't want a squib leaving a wad in the barrel, or irregular ignition causing goofy pressure spikes.
Since you are talking about using this load in a damascus barrel, I recommend making up some 3/4oz loads and sending them to Tom Armbrust for pressure testing. He does them for a very reasonable rate. The cost of testing 3 shells would be negligible compared to a ruined barrel.
FWIW, 7500psi seems to be about the lowest pressure you can get with 20gauge. There are some Federal hull loads with 4756, and some Remmie loads with 20/28 and unique that give low pressures, but not really better than the one you are using.
The benefit of another combo is better metering of powder, as 800x requires weighing each drop.
Rob.
