Wow, this has really got off topic.
I don't look at histograms. They confuse me.
I can say something about exposing for noise. If you under expose and then correct in PS you will have way more noise than if you were to expose properly in the first place. The first supercross I shot with my 1D I made the mistake of doing this. I figured I could underexpose a bit to up my shutter speeds and keep the iso lower, but when I brought them back in PS the noise was very bad. Now I tend to expose to the right by 1/3 to 2/3 to minimize noise at any ISO, plus I think my camera meters on the dark side a bit anyways. Most of the shots I posted here were shot using a different style than I normally use. I picked an exposure that would make the background appear darker than normal, and let the flash expose the rider properly.