Thanks everyone! Yeah it shot with the 70-300L at 300mm well over 100 yards. Miserable, dark overcast day. To shoot at 1250 & f8 I think I was somewhere around ISO 640.
The bummer is that it's been cropped from 18mp down to about 4mp. But I think the detail and noise will still give me a good 8x10 print.
That lens is something else. I get sharper, more useable images at 300 than I did from 300-400 with the 100-400L I was using.