The straight wall cases have a larger internal volume. Think of the difference in the wed area of a piece of .308 brass vs .45ACP. Basically the same exterior dimensions. The Federal Gold Medal hull has slightly more internal capacity than a AA or STS. Because of that with the same load it would have lower pressure and lower velocity. With fast burning powder the AA and STS are more efficient. They are designed for target loads. The Gold Medal hull optimizes with slower burn rate powders and has more potential to do work with the larger internal capacity. If you use a Federal wad in a AA because the wad is for a straight wall case it may create a minor bulge in the case wall. If you use a wad for a AA hull in a straight wall case the smaller diameter of the bottom of the wad mat allow some powder types to migrate past it and on ignition it may not completely seal the gasses behind the wad when the powder burns. So in summation the AA and STS type hulls were designed for peak efficiency with target loads. The straight wall cases will be less efficient with target loads but have more potential to load heavier payloads at lower pressure on a top end hunting load.
