I thought about the 5000 series but I want the compactness of the smaller size and I really want HST for convenience. I had a '94 5300 that I traded last year for a 125 hp tractor. I had the 3720 already and was going to use it as the substitute for the 5300 and still use the 125hp tractor for big chores. We irrigate, and there was almost no mud a 5300 MFWD could not go through or at least push itself out with the FEL if it was in trouble. The 125 hp tractor with MFWD does very well but I don't mess with questionable situations because I beleive it could bury itself just because of the weight. The 125 hp tractor has been stuck twice in the past year but both times with an attachment on the back which creates too much drag. (Both times it was my brother and not me!) One time it took our 245 hp MFWD tractor to pull it out.
The 3720 has no clearance for mud and no traction with R4s. I wonder if it will make it across a mud puddle.

I am sure it will not pull itself across a flat muddy field with R4s. I use the 3720 to mow the grass, run augers, fix fence and lots of little jobs. A 5000 series is just way to big to mow the yard. Even the 4000 series is a bit big for mowing and the R1s are not the best for yards, but the grass in the yard won't win any awards for beauty any way. Most of the time, I haul my zero turn to the farm to mow the grass around the house but the 4000 series would work when the zero turn wasn't available.
I don't think the 4000 series with R1's will be any match for deep mud compared to the 5000 series. The R1 tires on the 5000 series are just larger, taller and will do better. I do find it amusing that the hp of the 4000 series is more than my previous 5300. However, the 5300 had plenty of power for the tasks it performed. If I needed power or more 3 pt lift, I have other older farm tractors to do the heavy work.
Thanks for the info on the clearnce of 15". Is that with R1's? That should be ok. The front tires will probably be buried any way at 15"s.
Do the 5000 series still use a dry clutch? My 5300 clutch lasted about 1800-2000 hours. Another reason why I am looking at the 4000 series with HST. I believe loaders are hard on a dry clutch.
What I really want is a 4000 series with R1 tires of a 5000 series!