With the G540, the keling 381 oz/in motors (KL23H2100-35-4B) would be best for the X and Y.
It used to be listed as a 318 oz/in, same part #, but they've upgrade it to 381 now?
I have the old pdf which lists it as 318.
They match the Amps (3.5) and Voltage (48) of the G540 almost perfectly so you will get the best results with them.
Would have recommended the 387 for the Z but if the 381's are really 381 oz/in they would be better.
The 387 has the same 3.5 amps but needs a higher voltage (64) to get peak performance.
You should expect 100 IPM for the X and Y and 60 for the Z.
I can nearly achieve that with only 40V and 3 Amps motors, and I have a little more mass moving around than most too. ( alright no fat jokes )