I've played with some standard thinner shafts, for the ones I used, the LD shafts in the 12.75, 12.5 mm range had lower deflection. But no way to know for any specific two shafts without trying them both. I am guessing the Joss shaft would have higher deflection than say a Predator 314 or some other similar shaft to that, so it may be close enough to your 12mm shaft where you could not tell the difference.