This is an essential trick that I use on the XD to make many games playable-- just wanted to add that on this device, changes to the emulated clock speed of the emulator and the multithread feature only work after you exit the game and start again. Took me a while to figure this when I first got the XD so though I'd point out.
That happens in most android devices, not only XD. Usually those options need to exit game and load again. I only use reduced PSP Cpu for GoW, which is bery playable that way, but ony for that game. Perhaps other games need it too, but most games I played in PPSSPP are fullspeed, even some demanding ones like Tekken 6.
PPSSPP is quite demanding anyway, even my GPD WIN runs some games a bit slow. Shield TV is practically the only android device that manages PPSSPP in an amazing way. In XD lot of games are fully playable though,