When selecting a wastegate spring, one of the most important things to determine is the LEAST amount of boost you want to run. The reason for this is because a turbocharger cannot run less boost than the pressure rating of the wastegate spring. If you want to run more boost than the pressure rating of the wastegate spring, you can accomplish that with the use of a boost controller.
So how does all this translate into the real world? Well, if you have a setup where getting traction is difficult, you would want to switch to a wastegate spring with a lower pressure rating. The lower spring pressure rating will allow for lower boost levels in gears where traction is a problem, and with the use of a boost controller, you can then run higher boost pressures in the gears where traction is better thus improving the drivability of your vehicle.
Depending on the turbo and exhaust system design, a wastegate spring can sometimes make up to three times more boost than what the spring is rated for with the aid of a good conventional electronic boost controller.  For example, if a boost controller is installed that can apply pressure to the top port of a wastegate, an 8psi spring can make 24psi or more, although we typically do not recommend running more than 2x’s the wastegate springs rating as this keeps the demand on the boost control device low.