Here is the Ultimate Guide to Horses in Red Dead Redemption 2. Every aspect is covered and explained in overly verbose detail.
Horse Statistics Dynamic Table
Along with this guide is a simple web-tool allowing you to see all horses with all stats and filter & sort them however you wish as well as much more information on horses and horse items.
Horse Saddles, Stirrups & Consumables Tables
These guide host 3 tables with the costs and effects of all Saddles, Stirrups and Consumables in Red Dead Redemption 2 to allow you to better make your choices.