I think  the spring you speak of would be FAR too stiff for gravel and especially snow.  Your car is light, for gravel and snow i would think ~200 would be alright for your car but the stiffer you get the worse it will deal with gravel and rough roads.  I think it would be even worse in the snow...Dont forget also that you need a strut to handle the loads on your springs.  

My spring rates for the STI setup I have on my subaru are 210/185 IIRC and thats plenty stiff for the gravel and my car is about 2850lbs