Brian, for me personally the deck pads with the pattern are hard on my feet. I'm not sure if it's because these create pockets that give a variance in foot support, but for me, the flat, soft pad works best and I notice a lot less "numb foot" when I'm paddling distance. I've also doubled the flat pad on my race boards which have helped me a lot.
I stand a little off set and switch which foot is in front of the other by about an inch. My race board has a completely flat pad, my all around board has vert front to back ridges and my surf SUP has a diamond pattern pad. If I'm standing for 15 or more minutes on any of these boards it starts to happen.
It seems like you're tried to remedy the situation on your own by trying different footgear. One thing I'd ask is how your feet are positioned on the board while you're paddling long distance? Long distance paddling is very different from sprint racing and it can all depend on your foot placement.
I'd also ask what type of deck pad you're using? I've had issues with long distance paddling and numb feet before and would be glad to share what I've done to avoid this.