Carl,
I did quite a bit of the road testing of the stem, bearings, dampers and springs.
The stiff standard springs are fitted to keep the standard forks in the "safe" area of the their travel, venturing out of this causes handling problems, so the geometric problem needs to be fixed (fitting the JE steering stem) before fitting the softer springs that go with the stem kit.
When you say you have softer longer springs do you mean the "D" springs, if so these can be fitted, they are actually the same rating as the shorter springs but don't use the extra internal ones.
Once freed of their geometric constraints the forks become much more sensitive to rider weight, as an indication of the difference, the standard springs are about 57lb/in, with the JE stem fitted I have 45lb/in springs in mine but I weigh 20 stone, most people are using 36lb/in springs, some even as low as 33lb/in.
Chris.