I was in a simular situation ... I am 6'2" / 220lb and recently got a KX250. I used to race a CR125 10 years ago, but if I raced today I would be in the 250 beginner class for sure. I also do mostly playriding, but will have a few cross-country & mx races thrown in.
Anyway, I referred to the race-tech website for spring rate recommendations. I went with .46's in the front, and let me tell you, those babies are stiff! Quite honestly, I probably could have gone with .44s and been better off. Since you are 30 lbs more than me, the .46s would be just right for you. I have only adjusted the preload on the stock rear spring, and that feels fine for now.
Have fun!
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1995 (fork leakin' & plug foulin') KX250