What do you considering the upper limit for ISO?

In article 7b2f8028-b706-490b-8850-3e47a19ad052
@o36g2000vbl.googlegroups.com, says...
Lets say you aren't pretending, like so many do that you can take
really good images at high ISO. Where do you draw the line? Canon
and Nikon are now boasting 100,000+ ISOs for their latest offerings,
the Canon isn't even FF! But lets say you shoot with a D700 and you
have the luxury of going with either 3200 or 6400 ISO. Can you
produce a shot worthy of keeping at 6400 ISO? Or are we just kidding
ourselves that the output at that ISO, or from any camera is
acceptable?
I shoot a D300. IMO, beyond 800 ISO I have trouble accepting the
images as really good. I'm talking about non-noise reduced raw
images. Sometimes, it's possible to use NR and not make the picture
look like crap, but the leeway is narrow.

Surely where you draw the line depends on what the image is of. If you
are attempting to produce a traditional landscape, then noise and grain
are almost certainly undesirable. If you are a photo-journalist and you
take that once in a lifetime photograph then it probably doesn't matter
how far the ISO is pushed, or what other technical errors exist, if you
end up with an evocative image. For example:
http://www.arthistoryarchive.com/art...g_iconic_che.j
pg is 'noisy' and certainly wouldn't be accepted as suitable output from
a wedding photographer, but it it is a 'good' image.

Mike