The discussion of the synthetic lubricant could be quite lengthy so let me add just a few short remarks.
Synthetic will tolerate higher temperatures without coking.
They have a more uniform molecular structure, therefore, being more true to the particular weight (30,40,50 or whathaveyou) as opposed to the dino oil which is an average of larger and smaller molecules for a given weight.
The shear strength is maintained to a higher temperature.
Also, if you need to pass an emissions test, your hydrocarbons should be lower.
If there is a down side to synthetic I do not know of it. I do know that the negatives I have heard are from those ignorant of what they speak.