Recommended spring rates do vary between manufacturer and also between vehicles..

In reference to HSD's fitted to Subaru's, they're generally very comfortable straight out of the box (in comparison to other coilovers), but specifying the 1kg lighter springs front and rear makes them even more comfortable.

For something thats going to be driven 90% of the time on the street, a decent set of lowering springs will suffice and cost you about 1/3 of the price!