I can't even keep up on the tractor sizes and models anymore.  It was much easier when they just changed the last 2 numbers on the tractor every 10 years and that was a new series, the first two numbers were basically the size.  I know deere had a big overhaul with the 8000 series tractors, which was fin changing the numering system, but they started out with the 00', 10's, 20's and 30's.  I with they would have stuck with that instead of the confusing R series numbers.  I didn't see as much change from the 8x30 series to the R series as we had from the 4x20 series to the 4x30 series and they kept the same numbering system then.