To each his own...I suppose it really depends on your driving habits and how much you want to protect your expensive engine and transmission. I learned years ago how fragile ATF can be when I towed a trailer with a 220S coupe on it for a few miles with a Chevy truck. I had just service the truck trans. After the tow I rechecked the ATF level and it was burned black. The ATF had overheated on the tow and was worthless. Quickly changed it and the trans seemed to be fine.

I think the synthetic is a good idea for transmissions, the numbers certainly pencil out better. The heat resistance of syn ATF is worth it in my book. As to engine oil, I also use M1 syn simply because I cannot afford unnecessary repairs.

The Ford Mercon V and GM Dexron III specs are very similar. The Ford spec is rated for a higher temperature so if your choose regular ATF, I'd get one certified for both Dexron III/Mercon V.

230/8