Might give Alliant an email and ask for guidance... I bet Ben can get you what you seek. Power Pistol and 158 LSWC's in .38 Special have been very good to me when loaded to +P specs, and PP has also has done very well for me in .45 Auto and 9mm with cast bullets too.
As far as Nitro content and lead bullets; I read all the time the two don't mix, but it does for me. In my experience, some of my tightest groups with cast/swaged bullets have been with high nitro content Bullseye and Unique. Bullseye has a 40% Nitroglycerin content, which is one of the highest around, and Unique ain't far behind as I recall. To my knowledge, Power Pistol is basically Bullseye that has been treated with certain chemicals to change the burn rate/pressure curve, and it still retains a high nitro content.
Proof is in the pudding, and a lot of variables exist that need to be tested to determine what works best for your situation... Another great reason to handload, and see what shakes out.