[pothole]

Thanks for that. God, very soft, which is really what I thought - you can tell they're very soft just looking at them.

I ran 650lb front, 550lb rear on my old BMW E36 2.8l coupe - that 450lb spring was just a left over spare, I had several sets. It was mostly a road car that I also tracked. Was obviously very firm, but I enjoyed it!

You wouldn't need springs that stiff on a Box as its centre of gravity is a fair bit lower. But those rates you quoted are very very soft. I suspect M030 springs are only a little firmer than the standard springs.

That said, as you say, that the soft part of the progressive spring, but looking at the springs I have in hand, I very much doubt they're more than 250lb at any point in the range.

Anyway, when you say still researching, are you not sure the numbers are accurate? The difference between the two kits is utterly negligible if your numbers are right...