Another on the 'not worth doing' side of the argument. 6.0 to 5.0 is not best achieved by soft stepping, but by replacement.
PX is a shaft which divides people. Some find it very 'boardy' and unplayable, others like it and find it smooth and easy to flight. Flex ratings in PX are based on shaft weight rather than shaft frequency, so sets of shafts can vary in flex terms. PX 6.0 is generally considered to be a bit stiffer than TT DG S300, and PX 5.0 a shade stiffer than TT DG R300. If you are interested in something else, KBS Tour Reg and Stiff are pretty much spot on PX 5.0 and 6.0 respectively.
I don't agree that Swing DNA is a heap of ****, but neither is it meant to be a once and for all shaft fitting. It analyses 4 key characteristics, the most important of which are swing speed and tempo, and suggests shafts as a starting point for a fitting.
Out of interest, do you know the numbers produced by your Mizuno fitting (a sequence something like 83, 4, 5, 4).
