What is the difference between the iPad Mini model numbers A1454 and A1455?

The comparable page you're looking for is: http://www.apple.com/ipad/LTE/. A1454 is used for AT&T and similar Canadian networks only, while Sprint, Verizon and overseas carriers use A1455.

All bands are also listed on the specs page:

• Model A1454
  • GSM/EDGE (850, 900, 1800, 1900 MHz)
  • UMTS/HSPA+/DC-HSDPA (850, 900, 1900, 2100 MHz)
  • LTE (Bands 4 and 17)
• Model A1455
  • CDMA EV-DO Rev. A and Rev. B (800, 1900, 2100 MHz)
  • GSM/EDGE (850, 900, 1800, 1900 MHz)
  • UMTS/HSPA+/DC-HSDPA (850, 900, 1900, 2100 MHz)
  • LTE (Bands 1, 3, 5, 13, 25)

It looks like I just didn't look hard enough.

http://www.apple.com/ipad/LTE/ has all the goods on the model numbers.

The iPad mini Cellular A1454 Model supports LTE bands 4 (AWS) and 17 (700b MHz). The carriers listed for this Model are AT&T in the US and all Canadian carriers (Bell, Rogers, Telus).

The iPad mini Cellular A1455 Model supports LTE bands 1 (2100 MHz), 3 (1800 MHz), 5 (850 MHz), 13 (700c MHz), and 25 (1900 MHz). This model is for Sprint and Verizon in the US as well as all other countries around the globe.