I am considering running Mobil 1 Full Synthetic in 10-30 in my L2501 when the time comes. I have always been very satisfied with Mobil 1, and I can't see why it wouldn't work well in my Kubota. Bought the tractor new in February and only have 11.6 hours on it, so I still have a while to go. I wont be using it much in Summer, and it gets wicked cold up here in Winter. It will likely take me until Fall to get to the first oil change anyway, so there's no rush in getting this done. I can't get the Rotella T6 up here...I have tried. I just hope the Mobil 1 will be up to the task.
I too am a fan of Mobil 1 - been using it for 30 years in all my auto's that don't burn oil. Make sure you get Mobil 1 for DIESEL however.....Mobil 1 for gas has a formula that takes care of gasoline blowby and the Diesel version will have a little different formula for the diesel blowby and all the other gasses and particles that can get their way to the oil.
Another thing to consider, IF you are going to run in a colder climate, YOUR best choice would run the 5 weight oil, the difference between a 10w and 5w is very visible at 20 F and below, remember, the first number is the viscosity of the oil, and in this case the lower the better! The last number is the protective qualities ONCE the oil is to operating temps. SO in a perfect world, a 0W-40 would be an excellent choice - and they DO make it! It would pour in cold like room temperature water, but once up to 200 F it would still have the productive qualities and viscosity of 40 weight oil.
Oils are getting better every year - the base oils and the modifiers are getting better too. My new car demands 0w-20......the tolerances on the new engines are so tight, like .00095 !
http://www.enginebuildermag.com/2013/03/bearing-clearances/
- that a higher viscous number WILL not get into that tolerance UNTIL it gets hot....not a good idea. As we all know, most if not all wear occurs when we turn the key, an oil that flows freely will make an already great engine last EVEN longer!
Also - the lower front number allows less drag on the engine, thus better gas mileage, we dont really care about diesel mileage - but the flowability of the cold start is worth EVERY penny to protect your engine.