As far as a split for 70 ish front, keep in mind that in one world the idea is to put more weight in the forward panniers. So you may be a little more balanced than a chart would suggest.

I think another way of looking at this is not so much from the will it break perspective, tires are pretty tough, but from the what do you want it to do for you. At 6'6", I'm guessing that is a reasonably fit weight. A lot of hefties want a comfort ride, however. I'm slightly hefty, and also a little arthritic. So I want a comfortable ride, but part of that is efficient. So all these factors are tunable. You get on the bike and you work it out. If you want small light slick tires for low rolling resistance, and also wanted a little compliance, then no crashing into curbs for you. Maybe you need to carry a spare. If you want to blow through rough trails on your tours, then maybe you need to move up a size, keeping in mind the performance trend towards larger wheels and tires these days. Maybe still slicks for rolling resistance.

At that weight, I would be giving considerable thought to the wheel build. Your are in tandem territory, and there are industry standard specs for wheels and brakes at that performance level.

Also, it is always easy to take a recommendation for some fat, thick, tire. but if you never try the lighter end of things, you will never know how it would have worked out.