Sam,

I have used Bellevilles in the past for High Load low deflection usage, and have designed the stacks accordingly similiar to these sway braces... (Interestingly enough one of the best texts for designing them I have is in German, auf Deutsch if you will)

But 25% max variability for a spring support is based on something or another and I doubt that adventures significantly above that figure will produce credible results.

Cars, trucks, and other things use coil springs for the same reason that make them nice for supports... quasi-linear behaviour and a lot of deflection criteria.

Meanwhile I look forward to the redesign contract.