Depending on your conditions, weight is good. I am surprised at how little I sink even when I have my loader and weights on (I have R4s inflated near minimum recommendations with filled rears).
If you are floating on muddy soil and towing something heavy, you are going to spin. However, if you are TOO heavy you are going to sink to your axles and go nowhere. Do you live in an area where you can see what other tractor owners do? Do you have enough confidence in your dealer to follow his recommendations?
The TC30 and the 3130 are VERY different tractors. We would need more info about your land and what you intend to do with your tractor to make more specific recommendations.
Mark