Hey it's Patrick, I wrote the Tangent/Canyon Strive article on electricbike.com.
Had some other things that required my full attention lately so haven't been following ebike stuff as closely.
Briefly:
One thing I can mention right off - if budget is an issue - is that you may indeed find the BBSHD at 72/84v meets much of your needs for less $. I am truly amazed at the performance of my 84v 'HD bikes, and the 3300w or so they put out is about 90% of the max power I find myself using on the Tangent bike anyway.
Plus u get the benefit of silence, which if like me you are riding on mixed-use trails, with hikers/cyclists/horses etc nearby, makes a big difference. Tangent is still king but HD at 84v is amazingly fun, high revving like Tangent (at 20:1) and subjectively provides 70% of the max power via butt dyno. Also about which reduction ratio to use, I didn't read your whole thread but I have used both 20:1 and 40:1. I have a slight preference for 20:1 (mostly offroad trail/MX style use). But I like each in different ways and actually think both ratios are not ideal; for me something in between like 30:1 would be perfect. 20:1 revs like crazy but is too tall to use anything much over 3rd/4th gear; 40:1 has amazing torque but is really, really short. And once you have a setup that can do 250ish pedal RPM (instead of 150), you will likely never go back.
Hardest part may be sourcing a well-made 72v pack, custom for your application. I ended up making all my packs myself b/c nobody offered the size/capacity I needed plus I wanted to make sure they were done right.
Tangent is still of course the King, but 'HD at 84v is pretty f'in amazing.