Hi kt,
Your husband is in a weight range that he may well benefit from an extra 3" of latex not so much because he needs it (it’s unlikely he will actually bottom out on 9" of latex) but it may well be a preference because the thicker mattress will be more adaptable and have a wider range between soft and firm which can be useful with higher weights (see post #14 here). The only way to answer “is it worth it” would be based on his personal experience. I would encourage you to have a conversation with both manufacturers you mentioned on the phone so you can have a more detailed conversation with each of them. They will both have much more experience and customer feedback about their specific mattress designs from their customers in similar weight ranges than I do and they will be the best source of more specific and detailed guidance about their own designs.
You would always have the option of starting with 9" and then adding another 3" if you feel it’s necessary (making sure you give some careful thought to the firmness and position of the additional layer or topper).
It would depend on the specific configuration you choose but the biggest difference would be that the SleepEz design has more individual layers which can provide more options to customize the mattress (or in some cases add some additional complexity) before and after a purchase.
Phoenix