Well, don't go buy a bunch of springs under 100 lbs. Something else has to be done before you do that. To get used to your chassis and figure it out, I wouldn't go over 200 up front. Maybe even start with a couple 200s up front to figure out how your chassis responds with less weight forced on the rear of the chassis. Where and how the chassis unloads will be more subtle, controlable. With your car as it is on your shop floor, have it in neutral and move it ahead by pushing on the back of the car with a few fingers. Now loosen the jam nuts and crank the caster back quite a ways, go behind your car again and push it ahead with the same fingers... it will roll easier (takes less hp to move the car foreward from your engine) Also view 2 invisible lines, the same length coming off the upper ball joints and where they would point on the chassis, this is the influence factor your steering has on the chassis and it's roll center. Also, a softer rear spring on the right rear than the left will allow the left rear control arm to drop more than the right, thus shortening the wheel base on the left side through radius swing giving you rear steer. Also, with different caster settings and the car on the scales, watch how the numbers change when you turn the front wheels right and left while on the scales... this should put you more in touch with driver input per reaction manipulation of the chassis.. LOL you have to know where you are at before you start adjusting !!!
~Gimp~