It seems that whenever I look at a driver, I find something to fix in it
In this case, while looking at TNZS, I noticed that some games, e.g. Insector X and Plump Pop, were quite obviously running at 30 fps instead of the normal 60. This makes a lot of difference in the smoothness, strange that nobody ever noticed. Anyway, this was caused by missing support for sprite banking, a feature of the hardware which was already supported by seta.c (the games running in this driver use Seta custom chips). It's now fixed so Insector X looks better than ever :) The improved emulation also fixed the various gfx issues with Kabuki Z.