Well, as mentioned, if you are going to be using a bar go a little shorter. If you are going to dune race it +8 or less will be a handfull. I run a 10 mill cub and I weigh 190. It has a +14 on it and you could flip it over on top of yourself every run if you wanted.
Paddle also plays a big factor in swingarm length as well. If you don't have much paddle, you aren't going to get traction w/an extremely long swinger. Weight, paddle, swingarm length all need to be considered together.