I've been happy with 4.10s in my 05 Rubi and 35s. Live at 9,200 feet and jeep to 13,000 +, here in central Colorado. Bought it new in 04 and had it in Moab, stock a number of times. Worked great there also with the 35s and 4.10s last year. I can still pull a steep mountain pass, Vail, Fremont, Monarch, Wolf Creek at 55-60. Lost around 10 mph on the passes going from stock to 35s. Can I live with that? Most likely as it's not my DD. At 7,000 to 8,000 feet on the flats it will do 70 - 75 fine in 6th and if you want to pass, go to 5th. Bet at sea level it would do pretty dam good as at 10,000 feet you've lost close to 30% of your HP, would love to run it at sea level with the 35s and see what happened. As a retired auto and truck repair shop owner ( son's run it now) I can regear the Rubi myself for a good price. I remember driving it home new on I-70 from Denver up to the Eisenhower Tunnel, 11,000 feet and thinking what a slug compared to cars and trucks I usually drive. Guess what I'm saying is it isn't a hell of a lot worse with the 35s over the 31s. Will I ever regear, only time will tell.
My two bits on 4,10s and 35s again, Ron