Found this in a thread on PW. Comes from Yamaha support regarding the Grand Touch S compared to the NWX.
1) More grading of key weight between lower and upper register.
2) The fulcrum distance is the same as the NWX/GH3X keyboard, but the fulcrum of the white and black keys is in different locations, similar to the keyboard of an acoustic instrument.
3) Stability with full keystroke gives more control over expressiveness."
Further explanation evidently pointed out that the white keys are that same length/piviots as the NWX, but the black keys have been staggered/extended. So the action should have a different feel overall due due to enhanced grading and longer pivot black keys.
Since Roland does midi better than Yamaha I'll stick with the FP90X for now and enjoy the PHA50.