I assume you're talking about an 8boss run, right? If so, I may have some pointers.
For getting Zero, one possibility is to go to Turtloid's secondary area, cause that place has the Reploid with Hyper Dash and Z Saber Plus. The downside is that's a long trip, and I don't think you can make up that lost time with just quicker dashing.
Ideally, there are Nightmares you want to avoid. Turloid's rain, Player's blocks, and Scaravich's blocks are the prime offenders. So you'd have to either undo those effects quickly, or just do those three bosses as late as possible. Putting Turloid off is a very bad idea, though, as Ensuizan is very useful, if not only for the
invincibility glitch.
Many parts I'd imagine would be identical to FF's 1boss, save for maybe being able to equip some parts. For the rest, I imagine Zero would get far more use than X. The only other place I could imagine X being faster in is Heatnix cause it takes Zero a long time to kill all those minibosses, even if you can manipulate Rekkoha to kill them in one use.
Finally, it might be better to try to first get rid of the bosses that cannot be SDC'd. Guys like Mijinion.