Retro PI on the PI4 gives us:
Dreamcast
Better n64
PSP
Retro PI cannot do Dolphin-Gamecube because it's 32 bit.
No PS2.
PI3 -> PI4
The Ram capacity and speed are much better (DDR2 1GB -> DDR 4 4GB)
CPU/GPU is faster but not by enough to even handle N64 perfect.
USB 3 Disk Transfers speeds at 100 MB Per second VS 20 MB Per Second on Pi3 over USB 2. So this is one area that is MUCH better.