The non ball bearing version needs a converter that can flash stall to least 3400 to spool it up decently. However, the dual ball bearing version really only needs a 3000 flash stall converter. My buddy Don Mudrich currently runs the Dual Ball Bearing version on his GN, he has an Art Carr 9" non lock up 3400 stall converter and it spools this turbo (PT6776RLHP) instantaneously.
Like all P-trim turbine wheel equipped non ball bearing turbos, 3400-3500 stall is the general consensus. Dual Ball Bearing is a whole other ball game. Pardon the pun. 3000-3200 will definitely get the job done right.
HTH
Patrick