I've calculated aluminum wire 2AWG at 850' 20(????) amps over distance like if I want to power up a table saw for example at the end. Then I get voltage drop which leaves off 156 vac at the end.
Voltage drop does not work that way
First, voltage drop is based on your actual load, being drawn at that instant - not breaker trip. (much as the wire salesman would like you to base it on that lol). So stop using the number on the breaker to compute voltage drop.
Voltage drop is variable based on current - here is the formula, with E being voltage drop and I being the instantaneous current you are using right now, and R being the (unchanging) resistance of the wire:
E = I R
R is constant, so as you can see, E (voltage drop) is proportional to I (current being drawn). So you spin up your table saw, your net voltage plunges to 74 volts then rises right back up to 227 volts. As you're moving work through the saw, it drops down to 156 volts. You hit a knot, and suddenly it blips down to 117 volts. It's all over the map.
So your whole idea of engineering for a fixed, static voltage drop is a non-starter.
Sometimes, you can fake it
If you have very specific loads that you understand, you can just lump the voltage drop. For instance if I knew you planned to run 200W of hardwired lighting, I would tell you to run 14 AWG @ 240V. And then use LED bulbs with switching power supplies, which accept anything between 100V (Japan) and 240V (UK). So it sags to 140V, nobody cares.
But usually, you can't "fake it" and accept a highly variable voltage drop like that.
Either use transformers or throw aluminum at the problem
Now you have to make a costing decision. You start by deciding how much ampacity you actually need to support due to your loads. First, you must breaker at least 125% of your planned load. If your max load is 16A you breaker for 20A. That means you only calculate voltage drop on 16A, not 20A. Second, if you have specific actual loads in mind (34A hot tub, say, and 125% of that is 42.5A so you must breaker for 50A), then you calculate voltage drop on actual 34A, not 50A breaker. Got that?
Second, as you correctly surmised, 3% is bullpuckey. (except in Canada, you must beat 3% on the number I discuss in the last paragraph; on the upside, Tim Hortons). In America, you are allowed any voltage drop you find acceptable, as long as it doesn't contradict equipment instructions (NEC 110.3(B)). I'm not going to lose any sleep over 5.5% @ max. But I'm not Canadian lol.
Once you've arrived at this, you can calculate it two ways.
First, you run the numbers with cubic aluminum. Punch your numbers into the voltage drop calc and play "what if?". And go hit a site like wireandcableyourway.com and price the called out wire/cable.
Second, see what Ed Beal has to say about transformers. Now there's one area I differ from Ed, who recommends 600V transformers. That makes sense if you're buying brand-new and large (50 KVA). But for small ones (2-5 KVA) or used transformers off Craigslist, 600V is enough of an odd duck that prices will be painful or availability will be scarce. Remember you need 2 of them. Your table saw will do fine with a 2-5 KVA 120/240--240/480V transformer, and I see those in the $100 ballpark on Craigslist often enough. Your "200A" requirement requires a 50 KVA transformer, which is a beast that probably sits on a concrete pad. Brace yourself, but remember, it's a costing game: this or stupid-fat wire.
If your wire needs are so stupid-fat that the voltage drop calc malfunctions, look for one with a "Parallels" option and put 2 there. You can also try 3 or 4. But paralleling requires very special equipment with a very special price tag, so transformers may start looking good again :)
Consider conduit, but not too hard.
The huge upside of conduit is that you can change or upgrade wires down the line (presuming you made the conduit large enough, which is a good idea given wires of this size).
The downside of conduit is it facilitates theft. It makes it easier for a wire thief to sneak in, slice the wires at the supply end, then at the remote end, hook a pickup truck to the wires and drive off with them. They slide right out of the conduit. Direct buried, they won't pull so well.