Cannot play large PGM games on WiiU

I am using the latest 1.8.1 rpx version. Large PGM games (such as Knights of Valor 2, The Gladiator) are not playable. I have tried FB Alpha 2012 and FinalBurn Neo cores. In FB Alpha 2012 core, RA crashes. In FinalBurn Neo core, these games can be loaded but freeze after starting. Small PGM game such as Knight of Valor is running ok in FB Alpha 2012 core, but has broken sound in FinalBurn Neo core. WiiU has 2GB memory, and it can successfully handle large NEOGEO and CPS3 games. I believe memory shouldn’t be a problem.