For us, the biggest factor to get us over to the 7531 Box was traction (or loss of) on slick tracks in 100* heat & 140* track temps, and on a small tire with a heavy car. Instead of fighting with smaller multiple stages & progressive controllers, we use the Timing Retard & Launch Retard & Ramp functions (Gear Retard also available) to leave with less power, but can bring the power back in as the track permits.
Like x289sec said, I now wonder why it took me so long to go to the 7531.
Good luck.