There springs are generally geared more for comfort but they do have the GF210 which has 8.8 / 9.1 spring rates. I had nf210s on my 350z and was happy with them but still stock on the 370. I think I might get GFs for this one. We'll see
Did you install the eibach arms at the same time as the springs? Maybe it could be the arms hitting on something. I'd check those to see if there's any type of damage on them.