just because they ran old tech components doesn't mean they were any good. For the times they were as good as it was going to get, but 6psi isn't really that great for a turbo, heck 10psi isn't that great for a modern turbo. I am not saying they weren't popular but the scienc back in the day of those old systems makes them trinkets as compared to the efficiency of the new stuff. It isn't the turbo that is largely the problem either, most of the time the turbo (even at 10psi) far exceedes the fuel delivery and ignition timing of a stock bike.
Lets put this in perspective...in an ideal situation ray jay kits are good for 10psi, in that same ideal situation a modern bike turbo charger is good for 15-25psi (being conservative). A lot of the drag bike and car stuff can get into the 30 and 40psi. Heck my brother's new GTI blows 23psi out of the turbo from the factory. If you can even get those old rayjays to spool up 20 psi, you are way ahead fo your ignition and fuel capabilities, and probably outside the flow capabilities of the cb750 head as well. Comparing the old way of doing things to the new is like comparing a stiff fart to a gale force wind.
If you like chasing 10 extra hp, constantly setting points, doing plug chops, and adjusting needles and jets then the old stuff at 10 psi is for you. At 6psi you are probably picking up just what a bore kit, carbs, and a head job would get you anyway, and they cost about the same.
As for your article, even the old stuff runs great when new, but it is more susceptible to slighest changes in fuel which can come from sitting, or going to a different station than you are used to. Even a slight change in points caused by normal wear can mean the difference between a solid ride and a religious (holy)piston.