Aeons ago, when we bought my Hotpoint 800 spin WM12, the saleswoman said something along the lines of "they do say faster spin washers wear out faster"...so, perhaps it's a commonly held belief that slower spins will save wear and tear on your machine. Consider also the fact that the Hoover, much as with any modern machine, will not proceed to top speed if it's not properly balanced: instead the maximum speed is reduced or the spin may be aborted altogether. This is to protect the machine - be it the bearings, the spider, the axle, the suspension or whatever. There has to be something to it!

Sadly, none of us are really in a position to run a set of the same machines with the same loads over a period of time to test out whether limiting the spin speed even with well balanced loads makes a difference to longevity.

Until someone from a test institute or in possession of a degree in physics/mechanical engineering (or whatever it is you need) chips in with the definitive answer, we'll just have to resolve to continue using our machines in the manner we see fit (unless, of course, we actively decide to solicit advice from others).