FWIW: Larger motors (usually) produce more torque. To do so, they use either more current and/or voltage to do so. As long as your electronics can drive them, then its all good.
For the Z axis of a standard i3 Prusa, you don't really need high-torque motors, especially since there's two of them (unless you're running multiple extruders). However because they're paired, I recommend that you use the same type of motors for both Z spindles to avoid issues.
Also I'd recommend you use the same type motors for X and Y, as it avoids cases where there is some small difference in the motors that causes weird issues (like circles and squares being stretched for example).
Note that the pair of motors you use for the Z and the pair of motors you use for X/Y don't have to be the same as each other, so if you've already bought motors you may be able to use some of them for your X/Y without issue, even if they're too big for Z. Also, different step angles for each pair aren't a problem as long as your config works. I've used 0.9 deg steppers on X/Y with 1.8 deg steppers on Z before with no issue.
