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I would say it also depends on shutter speed. At the faster speeds 1/125 and above, the difference between VR on or off when on a tripod diminishes, upto about 1/500 or 1/1000 above which VR is theoretically useless anyway.
Generally speaking, IMHO and based on all evidence I've read on the subject -- yes, VR/IS elements slightly degrade IQ. VR/IS adds a lens element (correct?) to the optical formula -- which is not exactly Super-Low dispersion glass. However, the technological innovations in optics has come SO VERY FAR that I would think any reduction in IQ would be almost non-existent in the top-end lenses. There's a reason Canon didn't include IS on their stellar 24-70/2.8 II which has NOTHING to do with weight or cost. If IS didn't reduce IQ then I fiurmly believe Canon would've included it to further show up Nikon's own 24-70/2.8 --- which was universally regarded as superior to the 1st version of Canon's 24-70/2.8.
Tcole . Like you I always left VR on, but at 1/45 with the new 80_ 400 @ 400mm it defiantly must be off on a tripod ( no I am not pixel peeping the difference is very noticeable