In reality even a top brand flooded cell battery is only good for a maximum of 5 years. While it may seem just fine, with a heavy amperage demand load on it, it will not deliver. reason being is the plates are shedding lead oxide with every charge-discharge (which is a fact of the chemical reaction taking place) and that lead oxide will decrease the amperage delivered and eventually short out the plates.
The Yuhasa group 31 I had in my one Kubota M9, lasted 7 years as well but It was never placed under a heavy load situation either.
My rule of thumb is, I renew every 5 years now, especially in the tractor that does wintertime snow removal. I buy all my starting batteries for a local big truck dealer that also has a repair facility and they go through a lot of batteries so their stock is always fresh and recently charged with electrolyte.
I pay little or no attention to what brand I use. I do pay attention to how new the battery is however. Something I don't have to be concerned with because of their rapid turnover. Big trucks demand a high CCA rating as well so the 31's I buy have a high CCA rating.
A 31 is a large battery, probably too large dimensionally for most of the tractors on this site.