Per your question, going on straight spring rate ratios isn't going to produce an equal result. The changes aren't linear. Secondly, while you're trying to keep the recoil forces the same, your proposed change is going to increase the forces of the slide going into battery. Which, are originally substantially more than the forces in recoil and resisted by the slide stop.
Exactly what are you trying to accomplish?
BTW, if you're trying to lighten the SA pull, the villain is probably machine marks on the sear/hammer and/or the sear spring.