My experience is that Mobil1 is good oil and it is all I run in my 2001 Tacoma but I wouldn't think that it would economically feasible in a tractor. Most synthetics that are primarily engineered for spark ignition (gasoline) engines only meet the CF spec for compression engines (diesel). For less money, you can meet the newer CH-4 and CG-4 specs with a conventional oil that is designed for diesel. If your mind is made up for synthetics already, you should go with a synthetic diesel grade oil like Shell Rotella synthetic.
BTW, I wouldn't recommend any synthetic oil that I have used for higher mileage vehicles since they usually make any oil leaks you might have worse.