Your test generally confirms what I've for so long, as the occasion arises, gone out of my way to point out - the incredible performance of the "little 50 who could" (see the beloved childrens' story about a locomotive for reference); this modest little lens outperforms most every outlandishly expensive rival. It is constructed so that it feels like it is in danger of falling apart at any moment, but it doesn't and, if cared for reasonably well, will last a lifetime. It focuses to 1:2 as is, and to 1:1 with a matched extender which I never bought. It's amazingly cheap, and, even wide open at f/2.5, is better than most 50's and really pretty darn good. Stopped down one stop or more, it will at least match almost any 50 made and exceed most in sharpness. The focus motor is not USM, plus the focus ring is skinny hard plastic and has a litlle bit of a wobbly feel to it in manual focus mode. Despite all these shortcomings, this lens, if you can still buy it new, is a steal at its selling price.
The OP's test shows that this little Canon can easily compete with even a Zeiss lens costing vastly more money. I've shot 2 x 3 ft. nationally distributed commercial car posters for one of the "Big Three's" ad agencies with this lens on a 1Ds3, and the client, more used to medium format, thought it was plenty sharp and loved it. It ain't perfect, but it sure is a great deal, better than the "nifty 50" f/1.8, the 50 f1.4 (at least at apertures under f5.6 or so), the 50f/1.2 L at most matching apertures and more, as well as the Sigma f/1.4. Check it out for yourself on the-digital-picture.com website test. True, you can't shoot at very wide apertures with that kind of nifty bokeh, but barring that, this thing is amazing. It was designed about the time when dinosaurs roamed the earth and used an old tried and true optical formula that was more likely laid out on a napkin rather than a computer monitor, but, it just works.
Well, more than enough said.