It's a personal thing, and I am sure some heavy-weights will chime in soon (I'm only 180#). There are some good vid links here (and on YouTube) to guide you in setting sag, but setting the rebound/compression damping settings is more of a feel/art IMHO.
I don't know what weight the spec engineers had in mind when they chose the spring weights for the shocks… but I suppose they're just robust enough for two-up riding with some gear - on asphalt only. Factor in rough off-pavment riding and it would be very easy to bottom-out, I think, given how soft & comfy the suspension is.
Have you read the manual? I just tweaked my set-up after rediscovering the guidelines there, and the bike handles much better now. Granted, you'd have to adjust for your weight, but I found it a good starting point. If you don't have a manual, you can view it on-line from Yamaha's website.
I have found you have to fiddle a bit to find out what you like/don't like before settling on a particular setting. Write down where each setting currently is before making any adjustments, then document as you fine-tune the feel to your liking. Change only one thing at a time, document/evaluate, then change another if you like. This way you can go back to where you were if you want.
Keep in mind, significant changes in ambient temp -as well as riding surfaces- may necessitate a little tweak in the damping settings to maintain the same feel/response. Keeping your tires tracking the surface irregularities is Job #1 of the suspension, your comfort comes secondary to that IMHO.