Mike,
I guess I should qualify my, admittedly, rather pedantic lecture :-) As you can tell from the brands I mentioned, some of which no longer exist, I was talking about the situation 25 years ago. I doubt, though, that all that much has changed, except for the fact that lube oils, in general, have gotten a lot better. Sludge deposits on top may actually mean that the detergent in the oil is doing a better job picking up the combustion by-products down below, but I'm not saying that with great conviction. So, if you are using a reputable brand oil and you like the way it behaves, stick with it. My point was simply that, from a lubrication point of view, the well-known brands all do about the same good job, and you might just as well pick one brand over another because you like the color or the way it smells. But then, I'm an opinionated old cuss ;-) BTW, for years I used re-refined oil because that was really good stuff -- everything a refiner could not afford to get out of the crude was removed by running it for thousands of hours in city busses and aircraft. When it was re-refined it came out so pure it was almost fit for human consumption -- well, not quite, but it was a lot gentler on the machinery. But, my source dried up.
What you say about paraffin aroused my interest, though. True, paraffin in the oil would make it more viscous, particularly on a cold day, but as soon as it heats up in the engine, viscosity would totally disappear, and the ability of the oil to lubricate adequately, right along with it. That's why in lube oil manufacturing, paraffin removal by refrigeration and treatment with chemicals is a major step in the process. Again, I'm talking about how it was done 25 years ago. Who knows what goes on now. Geez, that was another long-winded, bloody lecture, wasn't it? ;-(
Pax,
Bob S.