Sympetrum illotum
I wouldn't normally post this here. It isn't all that nice a photo. But it illustrates a point.
This photo has no noise reduction, was taken at ISO 800 at a distance of 25 feet and is a 5% crop of the original.
Two points, really; comparatively small amount of noise and reasonably sharp. The low noise credit to the 6D.
The sharpness is credited to the lens. Something to note though, the lens is stopped down slightly.
I have noticed that if I shoot at full open with the doubler on I lose a lot of sharpness. Even a 1/3 stop seems to make a noticeable difference.