Tensioning the screws on the bearing cups is easy on my 20" with a lightweight tyre.
I find it more difficult on my larger muni, as the momentum caused by inertia of the heavy Duro Leopard make it difficult to judge when the wheel is binding or free.
It’s easy to think that it is rotatling freely when in fact it is the weight of the tyre which makes it appear so.
How do others handle this?
Finger tight is just right…
When spinning the wheel off the ground it should go round at least 15 times is my rule for what is too tight. Try tightening with one finger on the end of a normal 5mm hex key and your thumb against the middle. At the point you feel that you would need a second finger to tighten further is probably good.
I basically do it enough that the cups don’t wiggle around. Mine are held on by nuts 'n bolts not hex-keys so it’s a bit harder to judge it as ‘finger tight’, a spanner can usually get them far tighter than that if you’re not careful 
I should add that I am more concerned about damaging the bearings, rather than any extra pedal power required.
If you pick the wheel up, or slowly spin it, as the rotation slows, you should see your cranks ‘pendulum’ (for lack of a better term). They should slowly rock back and forth until they stop. If the wheel slowly glides to a stop with no rocking, I loosen my caps until it does.
YMMV.
I just swapped my Duro for a Maxxis HighRoller so my daughter could have my 26er Oracle. I own a Schlumpf so I have both sizes of Park Tool ratcheting torque wrenches. Measured nearly 40Nm loosening the bearing cups. Must be all that blue (medium) ThreadLocker I put on them because I’m near certain I settled on just under 30Nm (which is just about finger tight) when I put that Duro back on last summer. Good topic. Looking forward to what others suggest.
There’s nothing wrong with a little bit of preload on your bearings; remember that when you are riding all of your weight is going to be pressing down on the bearing via the top bearing holder.
And that pushes the lower bearing holder away from the bearing; if there weren’t any preload, the lower bearing holder would be completely loose. You don’t want that - you want enough preload that it’s not-quite-loose while riding.
With proper preload, the unloaded wheel won’t rotate quite as freely as it might, but when you are riding that difference will disappear. So torque the bolts to the recommended value; it’s a lot more than finger-tight.
i usually tighten until the wheel stops spinning without doing a pendulum. I try to spin the wheel and if I can tell the bearings are actively slowing the wheel down, then I loosen until I can’t quite tell anymore. its more than finger tight for sure, but I don’t gorilla down on it, either. There’s space to play in there, I don’t worry too much about it.
You are absolutely correct, Mr. Impossible!
My personal opinion is that when you start tightening the bearing cap bolts, you begin to pull the imaginary straight line between the two bearings out of square, which is why the axle begins to slow when the wheel is turned by hand - it’s being put into a bind. In a perfect world, all the bolt pressures would be exactly equal, and the bearing caps would be welded perfectly to start with, and you could tighten the bearing cups as tight as you like. It would be difficult to damage the bearings themselves through over-tightening, being stout as they are.
So I just tighten the bolts so they “feel” like enough, and that’s it. (Except for the Schlumpf, which gives an exact number, and that one I follow, using the torque wrench.)