Prof,
A maximum run of 8 feet of the 18 gauge wire out to a track, would permit almost a 15 ft x 7 ft layout. I'm just a novice, but that's pretty big in my book. :-)
(Of course, I know that some folks have gigantic layouts, so that would be small to them. If mine ever gets that big, I'm running 14 Romex and calling an electrician to hook up the ends!)
Mannyrock