gpspm with NEON scalers and the accompanying version of gpspmgui have just arrived to the repositories. The option is called Filters and is independent from Scale. Scale3x filter changes to scale2x when playing in portrait. For scale3x you need at last 500 MHz, but scale2x (filter) + triple scale (scale) seems to be playable even at 250 MHz, if you want to save the battery and think that it looks better than with no filter at all.