The speed at which the shutter moves is the same no matter the setting. All you are doing is changing the delay. There is no wear difference. Cameras are not cars.
That is not entirely correct. According to Hasselblad,
"Mechanical components gradually drift out of tolerance through regular use - affecting focus, shutter speed accuracy, frame spacing and other vital functions".
Although one can argue that the wear affects all shutter speeds equally, I believe it is more correct to expect the fastest mechanical speeds of 1/500 to be affected more. In other words, shooting a scene at 1/500 and f/2.8 may not produce the same exposure as (theoretically equivalent) 1/60 and f/8. But once you do the test and you confirm there is no practical difference, then I do not see any further "danger" of shooting at the fastest speed.
The accuracy issue is a bit different for the OP's other example, 1/800. It is a combination of electronic and mechanical mechanisms, or as Hassleblad calls it "’mechatronical", and is, again according to Hasselblad, far more precise than mechanical shutters. They claim they use more stringent standards than ISO, and that, in fact, their 1/800 could be safely labeled 1/1000 according to ISO.
Hasselblad also claims that the effect of smaller apertures on shutter speed accuracy is eliminated by their True Exposure mode (i.e,
"if the aperture is small, the light opening is cleared a little earlier and closed a little later than when the aperture is wide open.")
Actually, Hasselblad has a pdf on the subject:
Shutter at High Speed.Hope this helps.
