I put the 13 0z on my RM and it does make a difference, but not what I expected. Not as big a change. I can wheelie much easier now without it flipping over, I noticed that immedeately, And it will Lug down lower without stalling, but I'm either downshifting or feathering the clutch before I hit that point anyway. In that aspect it will help keep you going when you are gonna stall the engine on a long steep twisty hill that takes everything out of you. It's a nice addition and I would do it again. I guess because I'm a spode, don't race, and ride a lot of tight woods, it was a sensible mod to make for me.
If you really want to tone your bike down you can loosen up the preload spring on the powervalve (exhaust valve). It's an external adjustment and only take a few minutes to accomplish. I think your bike will have the adj. externally.
Mine was set stock at 90 deg clockwise from zero tension. I've had it set at zero tension and 45 deg clockwise. Both made the bike run a lot flatter for low rpm woods, less tiring with still plenty of grunt. You can set it however you like and adjust it as you go. It WILL make a big difference if you want to tone it down and costs zilch. Look it up in your owner's manual and see what you can do. It could be the ticket.
Now with the weight on and 2 yrs riding behind me I have the PV set to stock. It comes in handy where I only have a short distance to pick up a lot of momentum and speed. You will eventually end up setting it back to stock with some time too.
Please Update whatever you do as I'd like to know what happens and your impression of the FWW and/or PV adj.
Chief