By the way. I load tested them. They're 5.something kg/mm but they're not linear.
load-of-bullshit tested them, more like. If you did actually test them then you fu*ked up the test; cos they're linear.
nope. The diameter of the coils is irrelevant, it's how much they compress under load, eg a 6kg/mm spring compressing 1mm under 6kg of load. I know this to be fact, having specifically asked King Springs, MCA Suspension, BC Australia etc this question, when asking about any difference of spring rate between the wider springs found on stock suspension and the smaller diameter coils found on aftermarket coilovers. I'm surprised you didn't know that, being an engineer and all.
pretty much yep, more a dual-rate spring rather than a true 'progressive' where the coil spacing more evenly changes top to bottom. You can see this on the Tein website where they list the different spring rates for the same springs. But still classed as a progressive spring.