All SPKs use the same shell mold, which will yield a 105mm ball of the foot width, have the same width power strap and size range (25-29.9MP). But here are some specs of each boot:
Pro Model - leather wrap, double density heel cushioning, padded spoiler, rubber toe insert, quick lace system, super moldable Custom Fit Pro liner, flex 110
Kaos - padded spoiler, single density heel cushioning, rubber toe insert, quick lace system, fairly moldable Custom Fit Sport liner, flex 100
Kreation - no padded spoiler, no quick lace system, single density heel cushioning, minimum moldable Autofit liner, flex 90
The Kaos is usually the most bang for the buck. Hope that helps.