I've used the tammy 90 and no way I rate it that high but not low either. It's a middle of the pack macro...and that is not a bad thing. I would rather buy an old 30D or 20D, XT or XTi, whatever and a Canon EF-S 60mm than own a Tammy 90mm. The EF-S 60mm is a sleeper and a bargain price wise. The Sigma 70mm is as good as the Tammy 90.
But they best macros I ever used were the MP-E 65mm (a true 1x-5x macro only lens), the Sigma 150mm next and the Tammy 180mm next...then the rest are pretty much all the same give or take the QC that day in the assembly line.
I am looking forward to finding some older K-mount macro lenses and see what they can do...I never use AF for macro anyway as the entire point is the magnification not the focus...well what I mean is, I set my mag first then move the camera into focus. So, for me even a focus limiter switch is somewhat not needed, but nice if you want to use your macro for other shots in a pinch.
I think these reviews select the 100mm range for one reason, Canon and Nikon push those as the 'best' focal length value so people buy them because compared to other f2.8 primes they are cheapish. Horses for courses though...I loved my Sigma 180mm but the weight got to be way to much for me handheld. And the more modern 100mm lenses never really "blew my skirt up". The Sigma 150 otoh is a god amoung 1:1 macro lenses with the Tammy 180mm.
I truly cannot wait to find my first old Pentax or whoever macro lenses because I bet they are as good or better than their $500+ counter parts made today. EXCEPT for the MP-E 65mm which is the holy grail to most macro shooters. One of my favorite macro shooters uses that lens on a 20D body and he is in the upper end of macro shooters anywhere. Think of the DOF at 5x...ZOIKES!! but man is it fun to use...just need to learn to use focus stacking software on occasion.
Thanks for the post about macro, it's one of my fav things to shoot. I sure would not say there is such a wide difference between the lenses they tested. I would really prefer if there was a way to do blind testing of lenses and bodies. Keeping names out of the mix...results might just be a tad different.
I wonder too if the testers were using AF all the time...I don't think any macro lens has a very accurate AF...that is why a large number of macro folks do it by hand.