I have EBC springs in my 02 Bonnevile and also Thruxton springs. Two of each. Works quite well with my 78 HP 904 bike. The EBC springs are slightly stronger than the Thruxton springs.
Trying to get just the amount of pressure required. Has worked well for me with the approx. 70 ft lbs the engine puts out now at the max. torque peak.
Another solution can be to put a shim under the spring(s), depending on how much torque you have. The one from a spark plug works fine for instance. But a shim cannot be much thicker than that or you get coil binding.