Mlux, it seems very clear to me that the 46cm is very close to the other bikes you ride, and all you need to do is to increase the stem length.
I am 5'10.5" and one of my most comfortable bikes is a 56cm with probably a 90mm stem, and another of my most comfortable bikes has a slightly longer toptube than the first bike, and I use a 50mm stem. I can ride both bikes day after day after week with no problems, so be assured that stem changes are completely easy to do, can make all the difference in the world for riding comfort, and despite what some people worry about, do not affect steering etc.
My surly troll with the short 50mm stem steers perfectly well with dropbars.
Your advantage is that if the LHT has a 70mm stem on it, you can easily put a 100mm or longer on it and this will open up your riding position immediately.
I can change out stems in less than 5 mins, and there are perfectly fine new stems out there for 25 or 30 dollars. You do NOT need to put a $100 or more stem on your bike, no matter what someone tells you.
You really have the advantage of needing a longer stem, to increase reach. I can't tell you how many times I've tried fixing bikes for women friends of mine who have been sold too large bikes, and there just isn't room to put shorter stems on.
I'm confident this bike can work for you.
An honest, good bicycle store will have a box full of test stems, and can easily and quickly swap out various ones for you, and you'll see how easily this changes how the bike feels. And as you know, a more angled stem can help bring the bars up a bit also.
Get back with photos when you can, side shots in riding position is best with hands on hoods.
Thanks
djb . I can definitely swap out this stem for the original, but I just realized I'll also have to swap the handlebars back to the original (I want to do this anyways, the bar on there now feels too narrow) so it'll take me a bit longer. The original bar is not as wide as the new one and thus doesn't fit with the 50mm stem.
The stock stem angle is nowhere near as steep as the one on there now. (I wish I knew what the angles were exactly, but I don't) So, longer stem but find one that allows me to keep the same steep angle? Will this make me any more upright? I don't think you can get any more rise or much more of an angle than the stem I have now.
So, in my brain, increasing my reach at the same stem angle actually means I'll be in an even more aggressive position. Am I off base here?
I also had a few folks recommend gravel "riser" bars to give me a few more cms up front too... Like that idea over any sort of stem riser or BBB extender... open to more thoughts always!