I've run both. I prefer Synthetic. The additives in the Syn oils have longer lasting properties. May be psychological but I feel the Syn shifts better. I also run the little bit longer oil filter. I have run the Shell T-5 I think it is blended, T-6 Syn, Mobil 1 10w40 and V-twin 20-50 in summer, Valvoline MC oil, and a couple others. The T-6 is my go to oil even on the Victory.