I ran the 08 808 last year. I liked the car but hated the balls falling out of the bearings all the time. This made me DNF all the time. It wasn't just me because all of the other 4 guys running the car had the same problem. This didn't just affect us locally it was occuring all over the world. This year I'm running the X6. I like the way it handles better and no bearing problems. However, we've had every car (4) break atleast 1 rear toe in plate. I suspect that on big air landings the 1 down toe-in plate hits the ground breaking it. The MBX6 is not near as tough as the X5r. The composite on the X6 is more rigid and brittle than the X5r. This makes the car respond faster but it makes it not friendly for new drivers or drivers that crash too often. on the other hand the X6 doesn't near wear as fast as the X5 due to the harder composite. I've said this many times before and again Xray pivot balls are crap. Slop develops after you run it once and gets worse the more you run it. I've had the 05 XB8, 06 Xb8r, and the 08 808 and the same for all 3.
unless Xray goes to a smaller bearing around the diff pinnion gear it will always be a problem. It's spinning too fast, generating that much more heat, requiring that much more maitenance, and will fail sooner or later. If the pinnion bearing fails it's not just one part like a broken toe-in plate it's the pinion gear, ring gear, diff case, bearings, bulkhead, and most likely rear center drive shaft and pin. I know this happened to my 808. They did not warranty it. I had the car for 3 weeks when this happened. For this reason save yourself the headache and don't go with the 808.