KW Variant 3: replace rear springs with linears?

I called KW and they were perfectly willing to give me data on the front springs (61mm ID, 200 mm length, 80N/mm) but are very cagey about the rears. They told me that the ID is 61mm but couldn't give me the length or any data on the spring rate curve. I pressed the guy a bit about whether it was more of a dual-rate or smooth curve and he threw me a bone and said it was more of a curve.

I'm searching around for somebody nearby with a spring tester so I can figure out a starting point for the new spring rate.

In the mean time: Has anybody tried this yet?

KW Variant 3: replace rear springs with linears?