I think that "catz" post is the most relevant to my situation. I am often pushing my RAW files to the edge to get more detail / color / contrast out of them.
So am I. Noise is simply not an issue in my prints.
As for "pixel peeping". I don't think that's what I'm doing.
It's exactly what you're doing. But I think there is an issue beyond that and it might be this:
If I try to crop this photo down _at all_ I can see the noise with the full photo being displayed (ie not zooming in) on my 27" iMac. And that's doing a pretty small amount cropping (like only including the whole church). If I go any further, like just the front half of the church... it looks like I took this photo at ISO 800+!
Your description is confusing. I don't know if you are viewing at 50%, 100%, 500%? What are you doing when you say cropping but not zooming in? It sounds like the more you crop, the more noise you see, which implies you are cutting up the photo and viewing those cuts at increasing magnification. But from your description I can't tell what that magnification might be. For all I can tell you're looking at the equivalent of 200" prints.
But even if you don't touch the photo at all and just view at 100% (pixel peeping), you are viewing on a 27" iMac. I love Apple's products, but I *** hate *** their screens for photography work because you cannot tone down the contrast and saturation no matter how hard you try. They look beautiful for anything else, but I think they suck for photography. Even after color calibration they do not give an accurate preview of prints. That's why I have a 3rd party monitor. Out of the box it had the over-the-top-candy-world brightness, contrast, and saturation that is the fad right now, but I could tone it down to match real prints.
So at 100% it's like looking at a 50" or 60" print but with the brightness, contrast, and saturation shoved up. I'm sorry, but you will see noise in a 60" print even from a 5D2, especially if you push those three variables over the top.
How anyone shooting landscapes would think that is acceptable is beyond me. I've cropped ISO 100-200 photos from my XSi _way_ down and been satisfied with the results (and I didn't have to apply any NR at all!).
Here is a screenshot of what I'm seeing on my screen: http://farm8.staticflickr.com/7166/6482020907_8689f39356_o.jpg
Again, I'm confused as to whether you are actually cropping, or just viewing at 100%. That sample looks comparable in size to what I see viewing the image at 100% in PS on my monitor, so let's go with that. You're looking at the equivalent of a roughly 60" print. Do you make 60" prints? If so, you will not be happy with any small format DSLR and couldn't possibly be happy with the XSi which would be mush at 60". You need either the MF 645D, or a pano head to stitch 3 frames from a DSLR.
You made the comment that other people will see the same on their screens. Do you often crop out 1/3rd to 1/4th of your landscape photos for viewing on 27" screens? Or do you frame the scene properly, maybe do a bit of cropping, but otherwise show people complete photos? Because even on an iMac screen a complete photo looks fine. (Except occasionally in Apple's Preview. At some magnifications it just wrecks photos. And it's particular scales to, because I've played with zooming and showing full screen and a difference of just 20% might result in the preview looking fine.)