best 10 or 12 ply radials in 9.50 30 *15

Hi everyone, I am a farmer in Northern NSW and have an old ford f100 which is our main farm truck(cheap, reliable, easy to fix and lots of grunt) It does quite a bit of heavy carting. With seed and fertilizer and occasionally pulling a bogie trailer as well. It has yokohama superdigger tyres on it at present in 10.50 /31 *15 these have been good and have got 55000 out of them. But maybe with the heavy work we do should put stronger tyres on it. I want to go down a size to 9.50 30 *15 because it is too heavy in the steering at the moment. As far as I am aware all common 4wd tyres in the above size are 6 ply. What can I get in a 8, 10 or 12 ply that will still be good in the mud and drive just as well as the superdiggers, wrangler ATR, or dueler ATs on the tar. The old truck isn't the best truck to steer on the tar. Like the titanic. I need something good, and strong but will still give a good ride and steer well. Cost not really an issue, just want the best for our intended use. It does 20% of its miles around the paddocks which are rocky black soil predominantly.
Has anyone got any suggestions?
Thanks Scott