GRJ, when I built my layout about 1992, I had a lowest level yard with many blocks. I also had some 18-gauge 8-conductor wire. So I used that from the control panel toggles. Figured I'd be having a hand on transformer throttle anyway, so could compensate for voltage drop. When I added DCS 10 years later, I had very poor signal strength, virtually unusable. I eventually removed the #18 & replaced it with #14. No more problems; great signals.
You may want to wire up one or two tracks and check signal strength under load.