Hello Dave, I dont think any of us have ever seen real data that can prove one oil is really better than another, at least not with firm figures. Some of us, and by the way havent heard from Mark lately hope all is well, think that synthetics are best. Some people think conventional is okay. My view is to use synthetics in everything. I dont use my tractor enough to really be hurt by the higher priced synthetics. I use Mobil Delvac 1 5w40 in my 4310. It costs about 21.oo dollars per gallon but I think it is worth it in case of say the motor overheats and you dont catch it immediately. The better oil might help reduce the damage, Hopefully at least. Probably the bottom line is that use quality oil, synthetic or otherwise , and keep the oil filter changed. Also use good air filter management. If you dont supply the machine with clean air nothing you do will keep it from eating its insides.
Happy tractoring
Greg