I like a 10w30 syn in my tractor. I also have an oil pan heater on mine along with the normal block heater. The thing i like about using something like the Amsoil 30w/10w30, it has no VI to shear. If you are worried about cold start ups, then just add an oil pan heater for a few bucks and solve that problem.
http://www.amsoil.com/lit/databulletins/g27.pdf
http://www.amsoil.com/lit/databulletins/g27.pdf