...there should be no question about this. If you care about your engine use synthetic oil, and on the other hand, if you really dont give a shit, use regular.
A typical "boil off point" for regular oil is 375 degrees F
A typical "boil off point" for synthetic is 525 degrees F
Look at the pictures below (from calesta's profile) and take a wild guess why the rods are broken and fucking WELDED to the crank.
This would probably not have happened if this guy was using synthetic. He was producing more horsepower than the rod bearings were designed to support, so they got hotter and hotter until they reached 375 degrees and all the oil boiled off, and the bearings welded themselves to the rods, and the crank continued on its normal rotation, which broke all the rods.
Whoa you didn't have to link the large size picture... I changed it up to show the thumbnail with a clickable large pic. This will also decrease bandwidth load on HS and on my server. That is a damn nice picture though, if I do say so myself!
not only does synthetic have a higher boiling point, but it also has a lower coefficient of friction, which means there is less heat to build up in the first place. This also means that your rings will last longer because less metal is being scraped off onto the cylinder walls, which means your engine will go longer without burning oil, which means more time between rebuilds.
The pistons are also cooled by your oil...so you add it up. Synthetic might not make much of a difference in your grandmas car. But the way we drive, it is an absolute MUST. We put a hell of a lot more stress on engines then they were designed for, so you need an oil that can handle the increased temperatures associated with those stresses.