Hi
I have the BXM32 on my BX23 and the combination is great. It is big and heavy, the tractor feels a bit tippy on any rough terrain, the 42 is much larger and I would be concerned with that.
I do think the BX42 without the mulching feature would be a good choice if you felt you needed the extra size. The 3" is fine for me, I use anything I can for firewood and I like the shredder for small branches,etc