Q regarding microstepping speeds

I'm trying to determine the ideal speeds to run my 180 oz/in NEMA 23
motors with a 8x microstepping controller and Turbo CNC.

Most NEMA 23 motors tend to loose power when driven faster. For
example, lets say we have a motor that looses power above 5000 pulses
per second in full step mode.

When 8x microstepping, does that mean that the same motor would start
to loose power at 40,000 pulses per second?

Best regards,
Keith