MESA 6i24-16 or 6i24-25 ?

I read somewhere that all of the standard Hostmot2 firmware would fit into the 6i24-16 version of the card. Can somebody explain with a real-world example when it would be better to buy the 6i24-25 version? Or is the -25 version just overkill?

Yes, a 6I24-16 is fine for almost any LinuxCNC application

(as an example of a current configuration that will not fit in a 6I24-16: ST36 = 36 step/dir interfaces, not something most people need...)