Depending on what I am trying to do, I use .515", .526", and .527", with the .526" getting the vast majority of use and being most accurate so far. I have tried .530" but I had to go down to a OP wad and T-shirt for the patch, and the .535" had to be a bare ball. My bore measures exactly .540" though. You said ".540 plus a few thousandths", and you may want to measure those "few thousandths" cause they can make the difference between you being able to get a cheap and current production Lee .530" mold or having to track down a out of production mold and paying collector prices like I did when I finally found a Lyman .526" that mine likes. Now with that .526" I just load it like it was a rifle, powder with a PRB on it, and get good performance.
I forgot to add. My .526" and .527" get equal accuracy, but the .526" loads much easier, and I use pillow ticking with both. The .515" I have tried denim and canvas, but still playing with that mold.