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Well, it's very subjective. The M9 is no high-ISO wunderkind, but it's not unusable if you're careful with exposure and f/1.4 or f/2 lenses are kind of a necessity for this kind of work to keep the ISO at this threshold.
IMO, many photographers are extremely noise averse because they're looking at images at 100% on digital LCD displays, which have a strong tendency to exaggerate the minute tonality differences of neighboring pixels with value differences of a few percent. Analog CRTs provide a smoother rendering and mask this effect, giving a truer representation of ink on paper, if that is your end goal. And viewing at 50% gives a more realistic estimation of appearance in print. Also, it's an 1100 pixel image, so you're not going to see all the nasties. And I didn't try to open the shadows, leaving them natually dark, enhanced in part by the naturally strong vignetting of the 21 Lux wide open.
If you get exposure close, then the M9's noise IMO is acceptable at ISO 1250. I've shot it at ISO 2500 and again, if you're careful with exposure, it's acceptable (IMO), but has less leeway for WB corrections and skin tones can suffer splotchiness. If it's bad, I'll just convert to B&W. If possible I leave it at 640, which was the case for many of the images from this series posted on the M9 thread, and with the 21 at or near wide open, results in a pretty creamy looking image. The only thing I usually do for ISO 1250 is bump chroma NR up to about 35-40 in LR, and leave luminance at zero. But for these images I applied stronger NR, about 25 points luminance, bumped luminance contrast to about 50, and about 35 or 40 chroma, both for the M9 and Canon 1DIV, which I used at ISO 3200. But this NR was only because for newsprint purposes we apply very strong sharpening to compensate for the ink bleed. USM is normally 380/1/2, and with this degree of NR, the images sharpened nicely with very little to be concerned about. I also do some of the PP work at the newspaper and had to process a stack of images from the other photographers that day shooting other venues with D7000s and D300s at ISO 1600-3200, and saw much worse luminance noise from those images.