The different frequency (field/frame rate) should be taken care of by having switched to the other crystal, the different resolution remains relevant. Not just

The different frequency (field/frame rate) should be taken care of by having switched to the other crystal, the different resolution remains relevant. Not just that, there's also less time to perform computations while in vertical sync in NTSC compared to PAL. (Both those things are also related to the frequency of the crystal, by the way.) But: Since the game originated in Japan, it was probably originally written for NTSC(-J) anyway, so my guess is that it makes use of neither the increased PAL resolution, nor the additional computation time.