I've never owned the shocks, just their springs.

I've generally gone slightly softer, or the same, for carpet and asphalt. But I've never run on very high grip carpet.
I haven't had grip roll for about 3 years, but when I did, I found that softer springs solved it instantly.
I found that harder springs tend to heat the tyres quicker as well but can make the car more 'edgy' to drive. The harder springs also seem to cause the 'ring of death' on the inside of the tyre.