Jack Mullen writes (but didn't sign his post):
"I'm puzzled by the references to 156# rail. PRR's 152# and 155# sections are documented in (prototype) engineering literature and vendor's catalogs, but I'm unaware of 156#. Is this just a typo that's been perpetuated in this thread, or was there a third heavy rail section on the Pennsy? My recollection is that the 152# rail was designed in the late '20s, and the 155# was an improved design dating from sometime in the '40s. Overall dimensions remained the same: 8" h., 6 3/4" base, 3" head width. The 155# section had a deeper, redesigned head and improved fillet between head and web.
Both sections were introduced many years after the the I1s type and other heavy power was placed in service. Obviously I1s could and did operate safely on lighter rail. The purpose of moving to heavier rail sections was to attain an improvement in service life that would more than offset the cost of the added metal. Locomotive characteristics, axle loads, gross tonnage, operating speeds, grades and curvature are factors that come into play.
FWIW 8" is around 0.092" in HO, so code 100 is about 9% oversize in height.. In O, code 172 is about 3% over (for 48:1) or under (for 45:1), so perhaps you should consider a different scale. ;>)"
So you are asking me to consider changing scales because my PRR Mainline will likely be laid with track that is not quite but close to 7/8" of a scale inch too tall? Nope, won't do it, "I'd rather fight than switch..." 3^)
Perhaps, the Pennsy in the forties didn't have the extensive amount of 155 lbs rail as is being expressed here, but no doubt as we moved toward the mid-fifties it was likely more extensive than is expressed here. I would tend to believe that coal hauling eastern railways were all making their moves in that directions for all the reason you mention. So I'll use the code 100 rail that I have collected over the years as well as the turnouts and crossings on my mainlines, weather them to my liking and add secondaries and sidings out of lighter rail when visible.