I think 25KHz should be fast enough for you even at 1/8 microstepping as that would mean you could achieve (25,000/16,000) x 60 = 93.75IPM.
If you find your motors are fine at that max Velocity and you want more then you can increase the Kernel to 35KHz and that would allow a theoretical max Vel of (35,000/16,000) x 60 = 131.25IPM
45KHz would allow a max of 168.75
etc etc
45KHZ may be the max your computer is happy at, some people can easily run 60KHz or even 100KHz but others can get unstable at anything over 25KHz.
Hood