On the theme that “Enough is sufficient” I remember that my old 1928 built TT replica had a narrow clutch (2 plates less) and that was fine until I got more power out of it. With modern plates, it would have been fine with less plates. If the Pearce plates are thicker, I would try taking out one of the thick friction plates and using two plain plates together.
For their “Works” racing machines, Scotts used a heavier pressure plate to reduce the known tendency to bend like a dish. In such case, the majority of the effort is applied nearer to the centre. I am sure we all remember our old school lessons about force x distance. Many years ago, I just screwed a thick plain plate to the pressure plate with brass 2BA screws and this made a big difference. If you reduce the dishing, you can gey more drive. If you get more drive, you can slacken off the springs. It may be that the springs were produced in response to complaints of slipping and made stronger, but that now with better plates they are too strong.
Just sharing thoughts again! Roger