From the pics I've seen of the Teins and H&Rs, they are progressive. Progressive springs are easy to spot because the coils are not spaced at even intervals. Very few aftermarket spring companies seen to make linear rate springs. I do know Suspension Techniques tends to use linear rate springs and sometimes Eibach will mix and match progressive and linear rate springs depending on make of car.

 

I have 20s (245/35), Dspecs, unrevised Z springs up front and Coupe springs in the rear....the ride is comparable to Stock...and can even get softer if I want it to (or stiffer for that matter).

When I ran the unrevised Z springs/shocks all around, the ride was horrible - choppy and rough. The change to Dspecs was amazing.

 

Do you have the stock sport shocks or aftermarket shocks. If you used the 06 350z springs they are revised which has a stiffer spring rate in the rear.

 

Tein H-techs are linear, only the fronts on the s-techs are progressive

 

I bought Hotchkis Linear Rate Springs, I like them. Dropped 9/16" Front, 15/16" Rear. Consistent much improved handling. Prior to installation I hated the way the back rolled over in corners. Downside? With passengers on board I've bottomed the rear suspension. I'm about to upgrade rear shocks to compensate.

 

I have the coupe 19s on stock non-sport suspension but with Hotchkis sways. I just got done putting them back in and taking the stock 215-55-17s off. It's a bit harder and a bit louder. But the ride is not affected much at all. The handling is now much crisper. For me, 19" is the largest I'd go. I don't want to run anything lower than the 225-40-19 / 245-40-19 sizes and I don't want to run anything wider (IMHO just ups the weight too much).

 

Im wanting to sell my 20s and get coupe 19s

 

G35 H-tech front springs are progressive. If you want linear H-techs, you need to get the 350Z H-techs. I have the 350Z h-techs, and the ride is very smooth.