I can only comment on the stepper in the first post as that is the same specification I have. No issues at 68V on that motor.

I can see what you are trying to do now you have laid them out but can’t really advise on the others. Best guess would be use the same percentage increase in voltage on the first motor as a guide to the percentage over voltage values to try for the other motors and compare corner speeds in the calculations.

But if you do it for real then get a second opinion before you burn up a motor ! You need help from the electrically minded on here . . .