No, Evil_Cartman has got it wrong. You can see all the filetypes explained at devrs.com/gp32
GXB - This is a GP32 program, generic. It can be run by Wind-ups or the GXB loader. Not compressed.
GXC - This is a GXB with an encrypted hash so it only runs on one SMC/GP32 unit. It doesn't includes icon and name (read on). Not compressed. Shows up in GAME menu.
GXE - This is the icon and name for a GXC. Unlike the FXE, commercial games have info and actual program code separated.
FXE - also known as Free GXE - A GXB with icon and name. It is NOT compressed by default, but mr_spiv's program 'b2fxeC' can generate compressed FXEs. Shows up in Free Launcher.
FPK - Cannot be loaded by GP32! You must File -> Install them from PC-Link, and then the PC-Link will send an FXE plus some images/sounds/whatever to the GP32.
ZPK - An FPK with encrypted hash so, like GXE, it only runs on SMC/GP32.
They all take pretty much the same time to load, except for compressed FXEs which need to be uncompressed first, but the time taken is very small. Edit - in theory, FXEs take a tiny bit longer as they are 'scrambled' with a weak encryption, but again, it's nothing.
- Rico
p.s. adding to FAQ