switching to synthetic

I've been running Mobil 1 in my family vehicles since 1980 and do it for 2 reasons. The first is that Mobil 5W-30 has a pour point of minus 40 deg where as conventional at that temp. is "tar" at minus 40. So lets say it's minus 25 outside tonight and the wife forgets to plug in the block heater. I can start the car in the morning and I'll have oil pressure immediately whereas conventional you'll wait 5-10 seconds which means wear. The other reason is that since "true" synthetic oil has a stronger chemical bond between the carbon molecules the oil doesn't break down, due to heat and load, as fast as conventional oil. For this reason I change the oil every 6-8000 miles and if I go over no big deal.
You still need to change the oil regularly since it gets dirty and contaminated with water and other nasties. Forget about increases to milage and horsepower because the salesman can play fast and loose with those numbers and are pretty hard to prove unless you're running a high horse engine on a dyno.
I never run synthetic in my muscle cars for a couple of reasons but mainly because synthetics will find every place possible to leak out of and do.

Terry