Choosing among HO/OO track options

SGMRSC offers three HO/OO track ranges:

There are therefore two main choices to be made:

Code 75 versus code 100
Flat bottom versus bullhead

Code 75 versus code 100

	Code 75 0.075" ≈ 1.9 mm	Code 100 0.10" ≈ 2.5 mm
Rolling stock compatibility	Flanges of pre-mid-1900s rolling stock may foul rail fasteners (chairs).	All rolling stock should be compatible.
Realism	Scales accurately to tallest UK rail (2.1 mm) but taller than shortest (1.3 mm) UK rail. Sleeper spacing reflects UK prototype	Scales taller than tallest UK rail (2.1 mm). Sleeper spacing is closer than UK prototype
Robustness	Slightly less but generally sufficiently robust	Slightly more robust.

Flat bottom versus bullhead rail

	Flat bottom (code 75 or 100) rail	Bullhead (code 75) rail
Prototype	Installed in UK since mid-20th century.	Installed in UK mid-19th to mid-20th century. Still found in older or less-used track and on heritage railways.

Use cases:

Goal	Recommendation
Realistic modern track	Code 75 flat bottom
Realistic older (pre-mid-20th century) track	Code 75 bullhead
Most robust track	Code 100 flat bottom
Compatibility with pre-mid-1990s rolling stock	Code 100 flat bottom

Independent advice:

Track Peco Code 100, Code 75, Bullhead, EM and P4 explained at Chadwick Model Railway | 66.

The Most Realistic Track Yet? Peco Bullhead OO Gauge Unifrog Track