suspension tuning + upgrades: your thoughts?

[xlr8tr]

Hello all, looking for some direction on spring selection. I'm new at playing with these kinds of things, so bear with me.

Current springs are eibach coilovers 275 lbs/inch rears, fronts are 350. The car is too soft: way too much pitching in all directions, major tourquing on launch. I have no sways front or rear, and shocks are koni's with no adjustments. The car does corner at the moment quite balanced at neutral throttle (with the usual fun when throttle added). Rear end is a straight axle 9" with triangulated 4 link. With the soft suspension and the 4 link there is TONS of rear steer with the amount of suspension travel at the moment .

I'd like to start the upgrade process by going to stiffer springs front and rear. How much stiffer would be a good first jump? 25%? 50%? I'm not afraid to try different ones, i was a bit surprised at how reasonable spring costs are. Eventually sways front and rear will be added along with adjustable shocks, but i want to go step by step on this.

Any and all thoughts and comments are appreciated!