If you have an 80mm fork now and you like the way the bike handles, why not replace it with an 80mm fork? Why the need to go up to 100 or even 120? Going from 80 to 100 or even 120 is not going to give your bike or you any more ability to do anything different than you are already doing. It will just make the bike steer slower and drop to the side faster on slow turns. If you don't hate your Judy TT off road, I would recommend getting the lighter spring and be done with it. Otherwise stick with an 80mm fork like the bike was designed for.