I think you can go straight to 129 steps for Pro.
The L* value tolerances we are using with this ink are way more exacting than even Piezo K7 as were are using some nifty internal software I build for making ink. So with Pro it will always be damn linear right off the bat (also this is related to total ink limit being fairly even all the way across and a slew of other factors).
I would validate current linearity with 129. It may be totally linear right from the get-go.
best,
Walker