I would agree that the shooting of 2 3/4 of known(Published, I guess?)Low Pressure in your 2 1/2"er would be fine , as Mr Bell mentions.
There are 1oz recipes for 4-5000psi.
For your 7/8ths I'd think you could find some grand, very low PSI data..good luck.
Go to the Powder companys web sites & browse their 7/8th loads,,,they all have data...IMR/hodgdon etc
Franc