Actually Eibach springs are progressive. And you can get progressive racing springs,
All Eibach springs for Mk.V and Mk.VI are linear. Eibach Pro are linear, Eibach Sportline
are linear and Volkswagen OE by Eibach are linear.
Don't get fooled when Eibach claims they are 'progressive' as they are not.
Ok, there are few car specific springs for mild racing purpose that are progressive.
Few. Very few.
All pure racing stuff is 60 mm and linear. If you think you need a progression you
have to mate two springs.
in fact it's used on the vast majority of race cars.
You're wrong mate.
That way you can get a softer car at slower speed corner with less downforce and a car that compresses less when hitting the harder part of the spring under high load/higher downforce levels. Bump rubber also play a big part too but you get the idea.
From theory this is correct and that's why some racing teams use progessive rates
(provided by a pair of springs).
Anyway bringing this back to topic I would go with progressive aftermarket springs rather than OEM TTRS springs for your application. Near 150KG more compressing those springs can't be good. Get some springs that are made to cope with that load originally.
Using TT-RS springs seems somehow like an experiment, if Jake wants to take
this small risk - why don't he?
I'd avoid any progressive spring, because they handle worse than linear rated
springs. That's why Eibach don't sell them for the Golf and why Audi, BMW and
Volkswagen supply their cars with linear ones.