The MTH and Fox Valley rail scales to a prototype section height of 8.83". Modern 115# rail is 6-5/8" high, 132# rail is 7-1/8" high. Then 115# rail scales to Code 100 in S scale. Problem is no high rail equipment will run on Code 100 rail, nor Code 125. For high rail wheels the MTH and Fox Valley are the smallest rails that work. I have some Code 125 rail on my layout for the TT pit rails and all the guard/guide rails on the bridges. It is so close to the .138 rail it looks the same on the layout. The most noticeable thing about the Code 125 rail is the railhead width is wider than the .138 MTH rail.
I have no issue with the appearance of the MTH rail on my layout, I know it is too tall for modern track but set in the scenery with the ballast detailing it looks close enough to scale.