Evo and GVR4 share a similar rear suspension motion ratio, Evo is a little over .7 and GVR4 is about .8 (how far the shock moves vs. how far the wheel moves). Generally, you see a similar front to rear spring rate bias on gvr4 and evo kits. Some of the more conservative setups like from Tein or BC use a slightly stiffer front spring. Generally speaking a lighter rear spring on a front-heavy car will net a better ride. The damper itself is a huge factor though. More on that in a second.
Square spring rate setups are ideal on the evo/gvr4 as a nice compromise between handling characteristics and ride quality. If you plan on putting a big rear sway bar on the car, best to stick to square spring rates or slightly front biased rates at first and up the rates or do other things to dial out understeer later as needed. A lot of guys have got into trouble going for the big rear spring rates AND sticking the big rear bar on there, which can make for a car that oversteers pretty easily when the weight is shifted forward, like when lifting off the throttle or braking.
For a GVR4, 6k, 7k, 8k square setups are all able to offer a level of compliance that is suitable for a street GVR4. The trick is with the damper. When you start getting into really high end dampers it will blow your mind what is possible as far as a smooth ride even with really aggressive rates.