The length of you stabilizer is less important than the fact that the stabilizer does it's job, which is to stabilize the bow. Find the weight you need by first having all the equipment on the bow that you plan to shoot with, quiver, etc. then put on a stabilizer of a certain weight. Graps the bow between your thumb and forfinger. Is the bow balancing? You can use less weight the more "out-in-front" or extended from the rise the weight is. Laws of leverage.
For example, My bow becomes balances with an 11oz NAP shock blocker stabilizer (6-7")screwed directly to the riser, however, my bow also becomes balanced with a 6oz Quiet Tune (about 2")on a 4" extension, because of the principles of Leverage.
You might want to consider both the weight and length into you calculations.
Good Luck