Here's one of the rigs that i'm fairly certain is running a 4.7:1 gearset in the crawlbox. (I could be wrong about that ratio) He also runs the Marlin Crawler upgrade suspension/steering setup to run 40" tires (which he's running in the video)
link:
https://www.youtube.com/watch?v=jv4etlECGq0&feature=youtu.be