For someone wondering what these differences are, here are some photos that I took in the last decade, showing the gull-wing cab on C44-9W with the next generation, Evolution locomotive, without the gull-wing cab.
This gull-wing cab is a unique detail on Santa Fe and later BNSF, C44-9W and possibly the BNSF AC4400CW.
Starting from the Evolution Series, the cab roofline looked similar across all ES44AC & ES44DC, locomotives. even on BNSF.
When I first saw them, in person, I found out through a Google search that ATSF ordered them, this way to get the corners of the roof to clear some loader, possibly for coal, for both Dash-8 & Dash-9, with the wider nose, North American Safety cab.
BNSF inherited all these Santa Fe models and despite patching the Santa Fe warbonnet scheme, with their logo or completely, repainting the locomotive into the contemporary BNSF colors, the C44-9W still retain these gull-wing cabs despite being in service close to 3 decades.
These are just my opinion.
Naveen Rajan