I am not sure what you are planning to do with the tractor but there is a big difference between the 2 you are looking at.
The smaller tractor will be more manuvarable, easier to haul, and easier to store. It has the Yanmar engine and is pre-emissions. My cousin has a 3720 he uses on 18 acres and says it does everything he needs it too and has been happy with it.
I did not see a loader on the bigger tractor. I personnally would not buy without a loader. This tractor will defintely pull more, lift more and get more work done. Not sure if it has the power reverser/shuttle shift or not (this would be a big one for me).
From the posts I see you create, you are doing a lot of trail clearing. I would think the smaller tractor would be better for that. Just eaisier to move around and use. Implements will be cheaper as well.
However, if I were looking at those tractors I would be looking at the 5045e or bigger HP 5 series with loader. You wont have any issues going over stuff and the bigger tires will add in the cushing going over rough ground. Also, implements will be bigger and more expensiove. Then you need to think about how you are going to be hauling these machines as well. Trailers and trucks are expensive if you dont already have the gear for it.