Hey DEVLDOG,
I am 300#, but running on stock swingarm length. I screwed the spring down 2 full turns and that beeotch is firm as hell !!! In fact my back has been sore for the first time ever riding a sport bike (8 Years).. I noticed a great improvement in sticking in the corners and she stays in the ground a whole lot better on acceleration, but I don't know if that would help you due to the swingarm extension.. It's worth a try before spending stacks of cash on something you may not need...
The good thing is.... If you need to upgrade, we got great sponsors and resources right here on the board...