"Kato HO Unitrack is very prototypical from a standpoint of rail height, but Kato N scale Unitrack is very oversize (but extremely reliable)."
Yeah,the smaller the scale the more tolerable oversize rail becomes. Even oversize N rail looks pretty tiny. S scale flanges are proportionally smaller than HO flanges so an S unitrack system using code 100 rail would be quite nice in appearance and operation. The actual size of rail doesn't matter as much as the attitude that one is using as close to prototype appearance as possible for the chosen scale while still maintaining reasonable operational ease. ...DaveB