Boost valve size just increases pressure on throttle change and in manual low and second. Increased pressure will do nothing but help the clutches or band hold. There is also a limit to how big a servo can be, so while Chris's servo may be larger than most, it can't be by much.
So the boost valve size shouldn't have an effect on your servo selection.
However,
My experience with the .570 boost valves wasn't good and I will no longer use them. The .500 boost valve seems to work well and I haven't had any issues with the machining on the .500 boost valves.