Food for thought.
You know, if you are open to gravel biking, go take a look. They are fun as heck, and if you get the 2x in the front, you will probably won't outrun your high end gearing in any meaningful way. Avoid the 1x setups. Good news- the 2x (what youd want) is usually on the lower / mid end $$$ anyway.
You can always go to narrower road tires than the stock 38-42c setup if you wanted too, then switch back to wider tires after your 100 miler.
Most road bikes have gone up in tire size so much 28c+ to the point where the line between a road bike and gravel bike can get blurred. A lot of times I have to get up really close to something to figure out what the heck it even is.
I haven't really touched my road bikes since going gravel bike. Most of the roads here are so bad, they are more gravel like anyways.
As for size, some of these brands do have 61,62, 64 size bikes---which most stores arent going to stock in house, but, I bet you could get one discounted mail order if you knew what you wanted. I see a lot of bike companies will have some online ordering and some sizzling great deal, BUT the only bikes left are the largest sizes.
You could also try what the local bike store has, and if you like the model, see if they can order the larger size for you.
You are a big dude. Unless you have some leg/torso discrepancy, it seems like one would be close.
Seriously- go ride some new stuff. Just to get a feel.
This is a random size chart I pulled off the net, ignore the circled items. Not every brand/model goes to 64, but there are a lot of 61's out there.
