In my 5DM2, I get a 3800x2500 pixel RAW file, which is just fine for up to 20x30 poster-size prints. How many people need to print larger than that? What I gain is far less noise at 5000 ISO, (plus my CF cards & disk storage go twice as far!
Respectfully disagree on two points:
1) 20x30" print from 3800x2500px image is only about 125 dpi. That's OK for viewing at more than arm's length, but not good enough for close examination, in my opinion. I rethink the size I want to print if dpi dips below about 200. 300dpi is considered ideal for print publishing. A book publisher I worked for a few years back started with 400 dpi with final output downsampled to 300. (I never understood exactly why that was, but the results in cookbooks were undeniably superb.)
2) Especially in demanding light conditions, you want the most information your camera can possibly gather for you. Use the full size Raw capture. Resist cheating the shutter speed upward and give the image all the exposure you possibly can while still adequately overcoming subject action and camera shake. This way, more detail and less noise will be recorded in the shadows. If the light is especially challenging and demands slow shutter speeds, don't be afraid to shoot 30 frames and end up with 25 of them showing motion blur. Most times you only need one image to be sharp, but do what it takes to ensure you get that one. (At a candlelight choral performance I shot last month, I shot over 500 images to have 43 images suitable for delivery to the client.)
The jury is out in my mind whether setting accurate white balance in camera helps with noise levels, but it does speed up post production. And while in post-prodution, use "just enough" sharpening and noise reduction and then output your final image at a lower resolution. For instance, I sometimes output my Canon 7D images at 11.7MP from ACR to reduce apparent noise.