I have, at times, tried to shorten the total time by starting on high, but I doubt it accomplished much. Last weekend, I had a large whole pork loin that I cut into three pieces and browned well on all sides in a pan and then stuck them in the pot with salt and sage. Starting and finishing in LOW. It still just takes a few hours.
But for recommendations on slow cooker issues, remember that old references and old cooks may refer to old slow cookers. Specifications have been changed at some point to bring food more rapidly to the target 140F. And that had created a lot of complaints about overcooking. It also accounts for the bewildering range of cited temperatures. At one time, slow cookers were intended to reach 140F on Low and a bit over 212F on High. Now, it's more like 200F and 300F. Properly designed, one hour of High should be about two hours on Low. So the lawyerly caution dictates the Low setting be so high, and that determines the High temperature. I would also assume that the instructions in a 1970's slow cooker cookbook should be followed with caution and checking the food at a little more than half of the recommended time. With undated recipes, the problem is not knowing the source.
Also remember that the basic models are not thermostatically controlled devices. They are simply two different arrays of elements of given wattages. The designers assume a considerable heat sink in the form of the food. And the unloaded cooker must still be able to run empty indefinitely without being dangerous. It's a safe bet that the Low setting on new slow cookers will get a normal load of food up to 140 during a theoretical safe time.
Don't take a blindly simplistic view of safe temperatures. With solid cuts of meat, the internal temperature is not much of an issue. (Rare steak, for instance.) And salmonella and trichinosis are killed at 131F and 135F, respectively, when held for any reasonable cooking time. 140F is not a magic temperature - it's just a fudge factor applied to a guess adjusted for people who might have inaccurate thermometers. Ground meat I didn't grind myself I wouldn't consider safe unless incinerated.