The best procedure is to tune your arrows to your bow so they are exactly the right spine, regardless of the weight of your bow. You start with a bare shaft that is close to the right spine, and then trim it, change the point weight, and adjust the nock point until it flies straight. If you are not familiar with this procedure, I recommend you buy the Masters of the Bare Bow series of DVD's, which you will enjoy for a variety of reasons, and look at Ken Beck's presentation on bare shaft tuning in Vol. 2.
If you are not quite ready for this yet, just buy a half dozen of the nearest spine according to the charts and start shooting. It doesn't really matter if they are slightly stiff or weak. You will burn through the first half dozen arrows pretty quickly, but save one that is straight so you can trim off the feathers, and it will be the first addition to what will hopefully become a growing collection of bare shafts.
BTW, this forum is for shooting form questions. Equipment (and arrow) related questions are better posted in PowWow.