32bit vs 64bit question

[TheDax]

64-bit builds can be faster on systems with AMD GPUs(according to solarmystic, iirc), but compatibility can also differ slightly between the 32bit and 64bit versions, so keep both on hand.

Your 2nd question is off-topic, but I'll answer it anyway: Dolphin is so demanding because it's emulating a 483Mhz PowerPC CPU and a 162MHz ATI GPU when running Gamecube games, or a 733Mhz PowerPC CPU, and a 243mhz ATI GPU when running Wii games, not to mention the Wii/GC's DSP sound chip if you're using LLE sound. If you're wondering why PPSSPP might be faster than it, it's because PPSSPP isn't as demanding: by default PPSSPP is only emulating a 222mhz MIPS CPU with a 111mhz GPU, and PPSSPP doesn't need to emulate the actual Media Engine DSP.

If you also mean why are certain games in the same emulator more demanding than another, the answer can vary wildly: It depends on how many polygons are being pushed, what sort of AI is running on the CPU, how the game handles textures, lighting, and geometry, and multiple other things. Another factor that can contribute is if the game is coded poorly, it can be burning a bunch of extra CPU cycles that aren't necessary, which on an emulator can slow things down to a crawl(see Pangya: Fantasy Golf on PSP, I doubt it's that slow because of the graphics...).

If I'm wrong on any points, feel free to point it out, I'm not a guru.