Normally, we don’t ask stepper motor’s highest frequency, we think the question should be stepper motor’s maximum speed.
Because it’s meaningless to discuss the highest frequency without regard to driver’s subdivision.
Below table are our motor’s Max. speed and recommend working speed for each size of motors:

Motor type Motor Size Max. Speed (RPM) Recommended Working Speed (RPM)
Open-loop Nema 6 (14x14) 1000 100-600
Nema 8 (20x20) 1000 100-600
Nema 11 (28x28) 1000 100-600
Nema 14 (35x35) 1000 100-600
Nema 16 (40x40) 1000 100-500
Nema 17 (42x42) 1000 100-500
Nema 23 (57x57) 1000 100-500
Nema 24 (60x60) 1000 100-500
Nema 34 (86x86) 1000 100-400
Nema 42 (110x110) 500 100-300
Closed-loop Nema 8 (20x20) 2000 100-1500
Nema 11 (28x28) 2000 100-1500
Nema 14 (35x35) 2000 100-1000
Nema 17 (42x42) 2000 100-1000
Nema 23 (57x57) 1500 100-1000
Nema 24 (60x60) 1500 100-1000
Nema 34 (86x86) 1500 100-1000