I know you like cocktails or you admire the bartender. But why you don't simply mix engine oils? WHAT IF?
One of the early synthetics used was a Polyalkylene Glycol. This was totally incompatable and would gel when mixed. This has not been used for years for automotive lubrication. All common syntetics used forengine lubrication now days are a Polyalphaolefin (Mobil 1) or a Dibasic Organic Ester type (AMSOIL). These are fully compatable with conventional oils. In fact Golden Spectro and AGIP Sint 2000 are mixtures of mineral and synthetic oils. It is always best to mix oils with the same rating (SG). This insures that the additive packages are compatable and will maintain their effectiveness. ... Robyn Landers (http://www.bajahill.net/oilfaq.txt)
A snippet from Mercedes-Benz User Manual: Approved engine oils (synthetic/ mineral) may be mixed. However, we only recommend mixing engine oils of the same quality grade and SAE class.