Intermediate Rider Here.
Stock 13 ZX6R.
I've set up the suspension to text book sag, then made some rebound/preload adjustments based on what I was feeling while out on track. Overall I'm satisfied with the bike.
However, I am a heavier rider (230-235 No Gear). I notice the front end getting light frequently, especially corner exit which causes understeer and lowers my confidence.
I'm interested in hearing opinion on only re-springing the front and rear to better suit my weight.
Side note: I'm signing up for YCRS in 2020 which I know will help.
Sounds like the rear is squatting and might need more compression. Check out this guide
I would not respring the stock rear. You won't have much adjustable range with the stock valving.
I have a 1.0 K-tech spring that fits the stock fork. PM me if you want it. It'll get you 9.5 in the front together with the stock one.