Hi,
OK, so when Freq is 10 you want Reload to be 0 and when Freq is 1200 you want Reload to be 64600. That's 64600 over 1190 or a reload value of 54.286 per unit Freq.
Code:
Reload = (Freq */13897) - 542
When Freq is 10 you'll get (10*13897/256)-542 = 0
When Freq is 1200 you'll get (1200*13897/256)-542 = 64600
Do not allow Freq to be less than 10, you'll end up with a negative value.

This is not perfect but it might work, at least you'll get rid of DIV32. If you use the exact reload values for Freq=10 and Freq=1200 instead of the aproximate ones it might get a bit better in between the two extreme ends.

By the way, the lowest possible interrupt frequency, when running at 40Mhz and without changing the prescaler is 152.588Hz which equals an output frequency of 1.69Hz so Freq should really only be allowed to range from 17 to 1200 for 1.7 to 120Hz.

/Henrik.