The red Williams spring is the highest, followed by the blue. I have the blue in F-14, I feel it is plenty sufficient and there's no real need to slam the ball through the wireform. In my Taxi I have the red spring, so I can get to 100K but occasionally a full shooter pull will go past it. I have no worries since I repaired my spinout with fiberglass and epoxy it is way stronger than originally.

This is one of those things you often have to fiddle with adjusting, usually just the shooter alignment. Make sure you have a good quality shooter rubber tip too, if it is spongy or cracked, forget it - you won't be getting max plunge power.

The spinout must not move either, if it rocks around a lot it will rob the ball of momentum. Wax the spinout and make sure it is clean as a whistle.