To sum up, for MY copy of this lens.... FANTASTIC. MUST HAVE. Sure I might rather have the Sony or even Sigma 500/4, but the Sony is unaffordable and the Sigma is not available in A-mount. The old Minolta is new enough to have pretty good coatings and no issues with CA in most circumstance. Good contrast. Not super speedy focusing, but pretty good - seemingly faster than my 70-400. I say "might rather have...." because the 400/4.5 is pretty darn hand-holdable - I most often carry mine on a rapid strap, with and without a 1.4 TC and find it no trouble to shoot with hand held. Don't think that would be the case with the much bigger and heavier 500/4 lenses. My copy is unbelievably sharp and with the matched APOii 1.4TC I find little to no loss in IQ wide open. Bokeh quite nice much of the time.
Having said all that..... there seems to be a lot of sample variation for this lens. For whatever reason, some people say their lens is not very sharp. For this reason, I suggest anyone buying this lens to either try before you buy, or buy from a vendor that accepts returns. It should be SHARP.