This is a very useful topic!
Digital Paradise, your examples are very nice, great job! However, your results don't look like they're any better than I could have done with CS5, and I want something very superior to CS5. I want to reduce chrominance and luminance noise significantly more, yet preserve far more detail. From some of the other comments, I'm beginning to wonder if that's even possible with "third party" software or plugins. I would rather not spend money on software unless it is clearly superior...since you can't legally re-sell it later, as you can photo hardware.
Maybe there will be a new generation of NR software this year?
For example, my cousin's 5D3 files at ISO 4000, via LR4 (presumably "better" than CS5?), were NOT able to reduce luminance noise much at all, without putting the slider well above 80%, which severely softened the image. The 5D3 seems to produce luminance with a very large grain, perhaps 4 to 7 pixels diameter (seems larger and more harsh than even the 1D4's files).
By contrast, my older crop camera produces luminance noise with a much smaller diameter (3 pixels or sometimes less than 2 pixels diameter)...so I am able to reduce this noise much better via CS5, even with the slider well below 35%. (Of course key to preserving detail, are the luminance detail and contrast sliders...and the chrominance detail slider.)
My biggest problem with CS5, is it will not reduce "color banding noise" at all, whereas Topaz supposedly does. I've also not seen any evidence that CS6 / LR4 are superior for color banding...
I disagree with the practice of sharpening at .5 pixel radius in ACR (in the hopes it will preserve detail downstream). It's far better to find the ideal radius and optimize that (without over-doing it), and then export to whichever program will do further processing. Also, the "detail" slider (maybe it's better to call it the "global detail slider"...in the sharpening section of ACR) is highly effective on images that are already very sharp. If an image is already sharp and also noise free, it's best to push the detail slider as far as possible, while using the sharpening slider only near minimum (besides making its radius as small as possible...which is not always .5 radius).