I'm surprised 12 inch diameter is a record. And, Zap, it looks like that ironwood you have still to cut is a good size....
I'm going to have to check the circumference of some of mine. While many just die when they are 6-9 inches in diameter, I have quite a few that are substantially larger than that.
The one across from the east side of my house, just by the woodpile and adjacent to a good sized maple (read > 30 " diameter), is about 11 1/2 inches in diameter at 5 foot height at this point. Its lowest branch is starting to die. It's way too close to the maple, but I couldn't cut it. When it does go, it will heat the house well and long. Ironwood is fabulous firewood, burns long and hot. I don't split any ironwood rounds that will fit in my stove door. Ironwood dries really well in the round, is usually beautiful and totally bug free. I always keep a good amount of really clear ironwood in the house and stacked in the basement. One good sized log in the back of my stove will burn for many, many hours. I keep mine for really cold weather, or really bad weather (when I don't want to go out to the woodpile to haul wood).
Have you ever counted the rings on a 9 inch diameter Ironwood? On my land, those trees are often 80 or more years old. Really dense, heavy wood. At some point, I'll weigh a few logs that I have had in the house, dry for many years, and post their volume and weight.
I have really shallow soil. Despite all my trees' very shallow roots, I find that the ironwood has a small enough crown that it seldom goes over in the wind when it dies. So I never cut an ironwood down unless it is somewhere where it is a safety risk. If I leave them standing, they dry standing, don't rot, don't get bugs. Eventually the very base, right at the roots, will rot and the tree will either lean way over or fall. Then, I go cut it.
Usually even part of the root system is still solid..the tree itself always is. And all the branches are always ready to burn immediately, as also, not unusually, is the trunk.
At the moment I have a big Ironwood at the very edge of the top of the cliff in front of the house, blown so it uprooted about four years ago. It went over about ten degrees and hung up in a large tree (that is gowing just a few feet down the cliff); it still has some roots in the ground. It is still growing well!!..and there is no way I can cut it without the entire tree going down the cliff...there is so much beautiful wood in that tree that it makes me sick thinking about it going down.