That's going to be a tough call, as I don't know your shock angle. If the shocks are straight up they'll need heavier spring rate vs. a 30 degree angle. Either way, I think a 150 lb. spring is too light, and might make the rear mushy. The 200 lb. should be close if the shocks are fairly straight up. What coilover shocks are you using? Do they have full spring adj. and rebound gas adj. also?
Here's a nice tutorial from Ridetech to help you choose the right spring rate: http://www.ridetech.com/info/spring-rate-calculator/