There is no point in comparing springs without knowing the spring rate
and the purpose for which they are being installed. Standard Jamex
lowering springs are about 30% stiffer than stock, fine for a quick road
car, but way too soft for a serious track car.
Progressive lowering springs are designed to have the closely wound
coils bind up during normal use. They are primarily there to ensure that
the spring stays captive under full extension. But binding of the wider
coils indicates you are not achieving full suspension travel, and you
should consider a stiffer spring.
With springs, the lower you go the stiffer the spring must be to avoid
bottoming out. Better to consult with a knowledgable suspension place
regarding your intended use
before changing anything. And
remember that roll bars, shocks and tyres are all part of the equation.
Oh... and yeah, I'm happy with the Jamex progressive lowering springs
in my 86

Fine for an every day road car.
Cheers.... jondee86