It is very clear that turbo spoolup relies on significant fueling as well as rpm. It stands to reason, that a TCM tune with good downshift logic is going to be very beneficial, as this is the surest way to get the desired exhaust flow. The problem can be that a downshift can take as long as a full second, in which time, fueling is inhibited for "protection".
I noticed, for example, that the timing tables imply only control over upshift, e.g. "4>5". Are there tables that sep control downshift time, 5>4?