I don't think a fast powder or soft alloy makes a huge difference. The alloy and load need to be balanced, same as any cast load.
The coating isn't going to make up for a too soft for pressure alloy. It also isn't going to degrade a load that already works.
The coating merely replaces the lube, it doesn't change the other parameters regarding cast bullet shooting. Balancing the alloy, diameter, pressure, and pressure curve still matters.