IIRC, SP had many of their earlier F7s originally built with 65:12 gearing until EMD improved their traction motors to make them rugged enough to handle drag speeds.

I've run an SW-8 with 65:12 gearing. It was one of the better switchers I've run and would try to pull almost anything without even getting close to short-time rating. The 50-55 mph maximum for this gearing was not an issue for the operations.

Because of the solid pinion design, you don't often see 65:12 any more, but I have noticed 64:13 being used lately on some meter gauge conversions. The 13 tooth pinion is removeable like the "standard" 62:15.