Bob, I am not sure what you want to obtain and achieve with the resulting layout. I will make a stupid statement, track is track, it just comes down to the appearance. All brands of solid rail track greater than .138" high will allow operation of both scale and high rail wheels. The ability to actually operate scale equipment on the track is dependent on the minimum radius the coupled cars and engines require. Some operate on R19 and some engines can require R36. All high rail will operate on R19.
The real issue is with the turnouts. American S gauge turnouts are supposed to accept both scale and high rail but good luck finding any significant quantity of their turnouts.
American models makes a code 148 track system. Their turnouts can be made to operate scale wheels with a minor modification. Visit tuveson.com to see Carl's beautiful layout using AM track. He also describes the turnout modification. MTH makes a code 138 track system but not 27"R turnouts. Fox Valley now makes #5 turnouts and flex track in code 138 that operate high rail and scale. .138 rail is the smallest that will allow high rail wheel operation.
I have seen two layouts made with American S gauge track. It looks good and the trains (all Gilbert) ran well. Given the realities of availability I would use the AM track since it has a lower rail and is available in any quantities. AM also makes crossings for their track. The problem with MTH track is they only make R20 turnouts for it and I have found those to not be reliable. There is also of course FasTrack from Lionel with .138 rail. My layout is MTH flextrack with hand laid turnouts.
