Opening a bag o'wasps with that question....
Chris is reknown for advising hard springs, I tried his advised setup of 450f/600r springs on my Nitrons and it was bad news for the type of B-road bashing I do, I now have resumed almost OEM spring rates after trying about 9 different combos of springs.
If you do 80% track then stiff springs maybe better, though not allowing your car to roll and pitch as much will affect grip and braking respectively IMO. Remember the geometry of the car deliberately changes as you corner and brake, for example the tyres gain negative camber when the car corners and is allowed to roll over, thus providing you with more grip. If you add strong springs you partly eliminate this...
As a very general theory, the stiffer you make your suspension, the more snappy you make the brake away point. I've heard of a local "suspension guru" (it's all he does and has done for many years) near here who even implemented a softer than OEM spring rates on a local VX220.
I've found through many many hours of tinkering that I prefer slightly harder (+30%) than OEM rear springs, and OEM front spring poundage. When I had the car setup with far stronger springs (eg 450f/600r), the car felt more go-cart like and was fine on smooth roads, but was like driving a tennis ball down a bumpy b-road with lots of pitching and twitchyness that made it scarey.
Edited by Nev, 05 September 2017 - 02:54 PM.