Dude, if you use a 2.0 rear spring and need some more on-power steering, use a 2.5. If I use a 2.5 rear spring and need more on-power steering, I have to use a 3.0 rear spring. There is no general "on-power steering spring"
Petit RC has some SX3 set-ups listed, so has the Schumacher website.
http://www.racing-cars.com/search.as...e1=prodvalue14
http://www.petitrc.com/setup/schumac...herCatSX3.html
As no-one here knows your track, we can't know what shock position, spring and anti-squat work best. So if you need more steering, use a harder rear spring than wat you're using now, or a bit more AS, or a less inclined front shock than what your car is set-up with now.
I like to keep my car as standard as possible, so except for the FAB and front alloy suspension blocks it is all standard. Imho you don't need the 7.5° blocks etc.
Post your set-up and then we can help, without your set-up all we can do is apply some general set-up tips.
On a tight and technical track (albeit astroturf), I found that the B-hole on the rear hub was great: offers more steering and controllable sliding in tight corners. A bit less rear toe-in might help as well. Don't overdo this, when using the plastic suspension blocks 0.5mm difference front and rear is enough (should be around 2.3°).