ISO 100 is sharp and noise free…
…as is ISO 200.
ISO 400 shows no great loss of quality from ISO 200.
By ISO there is the merest hint of softening, although it’s only really visable at 100% and above.
ISO 1600 proves perfectly usable – even at 100%
ISO 3200 is still holding up exceptionally well, with plenty of shadow detail retained.
ISO 6400 is the point where things start to go downhill.
The top setting of 12,800 is noticeably soft, but remains just about acceptable when scaled down for internet use.