"However it is said that in order to get the best speed, u need to ramp the CLK freq. "

I don't suppose that is entirely corrrect. The ramp is required to ensure that the stepper never "pulls-out" till it reaches the required rpm and deliver the expected TORQUE. And kindly note that the accelaration ramp time is a function of the inertial mass that the stepper is driving and the desired time to reach the final velocity. Thus if your final velocity is high ( best speed as per you!)then the ramp time becomes significant.

However in most cases when specific data is not available on the load inertia, we start experimenting with ramp times of say 50ms to 500ms and settle for the best based on the "feel" of it. Actually in precison position control applications with dynamic load variations, this is a major chunk of the whole calculations and modelling.

If you have difficuly in getting a ramp via code then one other option exists : Feed the clock pulses to the stepper via a Voltage Controlled Oscillator ( very easy to make ) and whenever you want to start / stop the stepper just the ramp / de-ramp the control voltage to the VCO. Far simpler and best for this kind of application.

Here is a link to one such VCO :

http://www.designnotes.com/CIRCUITS/sqgen.htm

Raghu