I too was originally concerned with higher currents and whether there
would be unacceptable voltage loss over the stock wiring.  But my
experince has indicated that the stock wiring will do an adequate
job in most cases.

It is important to note that: [A] The wires from stator to regulator
will operate at the full current capacity of the stator ALL the time,
due to the "clamping" or shunting nature of the regulator.  [B] The
wires from the regulator on out to the lights will only be flowing
current equal to the load of the lights (and any other accesories
people glue on).

On a 400 with the stator winding I described (3 layers deep of #18 on
10 poles) we left the main wiring harness stock.  Total output is low
enough that [A] is not a problem.  Originally this bike was intended
to run a 55/60W headlight, but testing with a 90/100W revealed that
this stator config had the power to do it, so we went with that bulb.
The only time the headlight is observed to dim slightly is if high beam
is selected AND the bike is idling AND the 20W brake light is applied.
This rewind gives a good bright setup, and no wiring upgrades involved.

On a 600 with a higher output stator (150+) we did upgrade the wires
from the stator to the regulator in light of [A].   The rest of the
wiring was left stock, and it too ran a 100W headlight, plus
intermittent brake, turn and horn loads.

So, if a person wanted to be super ambitious and minimize losses to
the extreme, then you could run heavier wire from the stator to the
big load (headlight), and relocate the regulator as close to the
big load as possible.  This becomes more important if you run a
massive stator and ever bigger electrical loads.  But for Joe Average,
the biggest gains with the least amount of grief are to be had by
rewinding an intermediate stator (3 layers #18 on 10) and leaving
the stock wiring (and regulator) as is.

Paul.