I may be wrong, but it is my understanding that Valvoline Durablend is essentially 70% All-climate and 30% Synpower synthetic. I've also read that Phillips Trop-Arctic and Motorcraft are 50% group II and 50% group III. Mobil 7500 is supposed to be approximately 80% Mobil 5000 and 20% Mobil 1 EP. I have not found anything about QS, Pennzoil, Supertech or any others. Prices vary, so I would calculate which is more cost effective: buy a blend off the shelf or make your own. Please don't take this as gospel; it's just what I've read on this and manufacturers' sites. One last thing: If I were to mix my own, I would stay within the same brand family.