I have used both conventional and synthetic oils.
The only benefit to using synthetic that I have ever experienced was the vehicle would start easily the coldest morning that I ever experienced in Mis-Missouri (my thermometer showed about -25 F.).
Power and economy increases may exist, and be measurable in a laboratory, but I experienced no noticeable increases.
Our last shop truck (non-stovebolt) that ran exclusively conventional oil lasted 440,000 miles and the cylinder head was never removed. Got tired of repairing the rust caused from the salt and cinders MoDot places on our highways so that below average drivers can be on the roads in the winter.
Just my experience, others may differ.
Jon.
