A few more highish ISO noise examples all taken with the 200-500 f5.6 VR.
Run through Noiseware noise reduction in PP.
I'd say more than acceptible for ISO45,600
1,100sec, f7.1, ISO45,600 handheld.
1,200sec, f8, ISO7,200 handheld.
1,320sec, f8, ISO4,000 handheld.
1,200sec, f8, ISO2,000 handheld.
1,200sec, f8, ISO9,000 handheld.
1/320sec, f8, ISO14,400