FreeSpeed Pro worked as advertised. The included instruction sheet shows DIP settings from 500Mhz to 1050Mhz in 50Mhz steps. Core voltage can be adjusted from 1.45V to 1.90V in .05V steps. There are no L2 cache ratio settings.
FreeSpeed Pro won't let you overclock your Athlon higher than any other methods. How high your Athlon can overclock is still determined by the quality of your CPU. FreeSpeed Pro is just a nice simple way to go about overclocking. Using the FreeSpeed Pro I was able to get my Athlon 550 to 700Mhz using the big Alpha P3125 cooler.