Just that they restricted the "wonder-engine" to matching the T56s' power levels.
This makes sense... work out how the big nacelle changes handling, and how the big prop affects airflow over the wing (and along the fuselage) before trying higher (and asymetrical) power settings.
Wind tunnels & computer simulations (which are totally dependant on the data [guesses] entered) only tell you so much... flight tests always tell you things the other methods didn't.