Tony L
Administrator
The GR-D is a 2.8 lens isn't it?
It's f2.4. I agree the Sigma is too slow, but a lot depens on how usable the higher ASA settings are. The GR-D is only really usable in colour to about 200 ASA before the noise starts becoming obtrusive, by 800 ASA one has to flatten the image to b&w to get an acceptable result. If the Sigma is largely noise-free at 800 then it would end up ahead.
Tony.