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It is true the pixel density is similar and it is on the APSc sensor that the lens struggles to produce a sharp image at the long end. It is worth mentioning that while the lens tests show it's best at F8 (600m) in the center, real world shooting at longer than test distances proves undoubtedly F11-13 to be sharper, this maybe being a function of the internal focusing. Even at wider apertures at the long end it's very sharp indeed at close distances.

 

 I have taken something around 10,000  images with the Tamron and on the D7100/ D750 and the one thing that has surprised me the most is, how well the resolution holds out to the corners (FF), you really don't get much sensation that things get softer away from the center.

 

 It certainly would be foolhardy to judge the 5D-R's sensor's characteristics from the Tamron especially at the longer end, but given the 5DR's history with lenses, that, as a body used for testing....    "any lens tested"....    is going to finds it's pants round it's ankles in the corners!  I  doubt that the Tamron will ever find itself on a 5DR and if it did it would soon be off again!  

 

   However, for these very welcome tests, the comparison between the Tamron and the Sigma Sport will be of great interest. Anyone who has tried to find an affordable tele-zoom that actually delivers sharpness, and the Tamron is the first that has achieved that accolade, (besting by a considerable margin my previous Sigma 50-500mm F4/6.3) will know that these lenses have opened up a new world that was otherwise left to the well heeled pro shooter carting around their $10,000 heavyweight bazookas.

 

 Therefore, 50Mps or not, we are on a level playing field, so bring on the Sigma Sport and it will be dueling pistols at dawn!

 

BTW.Weather sealing is only at the lens mount.

It is worth noting that the sharpening applied to the MFT images, skews the difference between center and borders, in this case especially as the lens itself is not tack sharp at this resolution. In other words, the center gets sharpened more than the borders (th nature of sharpening applied) and the difference seems bigger. 

In the sample photos, the lens seems to perform quite ok, even on the 5DS-R. And yet soft enough to avoid the worst aliasing