if you are using libretro glupen64 as emulator you can switch the resolution in the retroarch menu. This emulator performs very well on my xu4. if you have sound issues change the sound driver to sdl2 and the resampler to sinc. i have disable the recording driver.
IMPORTANT! Make sure that in you gamesettings rewind and shaders are disabled. Without disable this you get 1 frame per second.
this is the first emulator what make it possible to play mario tennis.