The slowdown is a bit odd. The plus 4 is using basically the same CPU as the arcade cabinet and at a higher clock speed (1.76mhz), though presumably it has to get involved with the graphics while the arcade cabinet had the vector graphics unit.
Why do they not have a ZX [space] ./ control scheme? It would mimic the arcade control panel fairly well. The monochrome version should be able to run in a higher resolution and better emulate the vector graphics.
