Spring rate vs wheel rate
Most suspensions mount the spring somewhere between the chassis pivot and the wheel, so the spring moves less than the wheel does. The ratio of the two is the motion ratio, and the wheel feels the spring rate times the motion ratio squared. A 400 lb/in spring at a 0.7 motion ratio is only about 196 lb/in at the wheel. MacPherson struts sit close to 1.0; double wishbones and multi-links vary a lot.
Ride frequency
Spring rate alone means little without knowing the car's weight. Ride frequency combines the two: how many times per second the corner would bounce. As rough guides, about 1.0–1.5 Hz feels like a comfortable street car, 1.5–2.0 Hz a firm performance car or autocross setup, and 2.0–2.5+ Hz a dedicated track car on sticky tires.
Front vs rear
Many road cars run a slightly higher frequency at the rear than the front so the car settles flat over bumps at speed. Use this calculator on each end and compare.