Spring rate for rear coilovers

i had 150 pound qa1's on my dart for a while. they were perfect with just me in the car. but when loaded for a trip and the family in the car they wern't heavy enough. went to 200 pound springs and they were a lot better but the car still sags quite a bit with everything in it (4 of us,a tool box,floor jack, spare tire,extra parts,chairs, stroller, pota crib and stuff to last us on a 5 day trip.) so now i'm gonna give a vari-rate spring a try. 175/350 pound spring. i think they will give me what i want. i know for a fact the 175 will be good with an empty car and the 350 should be good when all loaded with the family. we will see soon enough i guess.. :)
http://qa1.thomasnet.com/item/motor...75-350?&plpver=1001&bc=1001|1005|1037|3001134


with the different springs i have tried it seems easier (to me anyway) to get a heavier spring( within reason. 500 pounders sound way too much to me..) and go a click looser on the shock. it gives me a good ride but still handles great on the street. i'm sure if i was going pure track i would probably want heavier springs and the shocks set stiffer but my car is a family street car so thats how i set it up.


what are you running for a rear suspension? i have the street lynx from rms. not sure if that changes what you would need spring wise ?