that first dyno run at the beginning of the thread just does not mesh; the second sets look much more inline. The 366 should get a bit more power than the 38r but should spool slower as well. You go from a BB to a JB and go from a smaller Turbine wheel to a larger all points to a slower spool given how close the housing AR are to each other. While the larger wheel should move more air is the designs are close you still have the same size comp wheel per RPM of the shaft. It should keep BP lower for a given comp pressure but I would think you still have comp wheel design and cover to deal with. Without maps of the comp and turbine its all a WAG IMO. Get it back on the dyno with the 38R and see what she does. My uneducated guess is 25hp more for the 366 if the fuel is there is the program. To do it right they would both have to be live tuned to really see.
I would guess 475 38r 500 366