I have a few Atari vector games implemented in FPGAs and those you can easily clock much, much faster or slower than the original clock rate and since the video hardware does not require any specific timing, it can deal with it just fine. Using an analog scope as a display I slowed it down to the point that I could watch the beam dancing around tracing out the various objects on the screen in real time, and then sped it up to about 30x the regular speed, a magnetic deflection vector monitor wouldn't have kept up with that but the scope can.