the stock rear spring is a 5.4 and is good for about 200lbs you should get a 5.7 to 5.8 the problem with using the stock spring is that you will have to put allot of preload to get 100mm of rider sag, then you will end up with no bike sag this is not a good thing, also with the lighter spring it will tend to ride lower in the stroke and therefor feel stiffer than if you had the correct spring holding up in the stroke.
