OK. So what you're saying is that the more balanced the two circuits
on the double pole breaker are, the less voltage drop I will have.
Theoretically then, if I had a 250' run with two outlets at the end of
the dual pole 20A breaker (one on circuit 1 and the other on circuit 2)
and had a 15A load on BOTH of them I'd be OK. But, if I removed ONE of
the 15A loads, I could be in trouble because the voltage drop would go
up and drive the load way up. Correct?

I think I could balance the load between circuits but I can't guarantee
it would be that way all the time so that may not be the best option
for me. Also, 10AWG wire will still have a high voltage drop for a
250' run (based on the voltage drop calculator using 120v).

What if I have two separate single pole 125' circuits using my 12-3 and
two 15A breakers, BUT, I combine the two hots of the 12-3 to make it
12-2 inside a junction box just before going into my circuit breaker
box (12-2 would be going into the box connecting to the breaker) and,
along the run, pigtail the two hots of the 12-3 together to look like
12-2 inside the outlet boxes. I will then have a very low voltage drop
on my 125ft run because the two wires of the 12-3 are combined. It
seems this option would get me the resistance of 8 or 9AWG wire while
at the same time giving me the shorter 125ft runs.

Thoughts? Dangers? I know if one the splices where the 12-3 is
combined to look like 12-2 fails then load & resistance will go up
driving up the load. But, that would be on an outlet by outlet basis (
I could even check it with a meter) and the 15A breakers would limit
risk somewhat. This method seems safer to me than trying to guarantee
I have the balanced double pole circuit option described above but
maybe I'm missing a potential problem. Thinking about it, it looks
like I'd have to join 4 12AWG wires together with a 12AWG pigtail for
each outlet (making 5 wires) inside a wirenut. That might be a
problem?

Thanks again...and I appreciate your feedback greatly.

Kevin