Well that is good to hear since I have never used the 5D. I guess will get the 70-200 F4 for the future 5D, and maybe by that time a newer version of the 5D will be out with better ISO performance...I can hope cant I?

With the latest version of Topaz Denoise you can actually unblur, and recover detail. You can also reset the black point with it. I don't think there is currently any better plug-in out there for denoising.
And then with Nik Viveza you can get selectively colour back, if so required.
This step, or occasionally two steps, will even make a one-stop underexposed iso 800 G10 image look good.
You'll have to play a bit with it to get it perfect, and then save it as your own style/theme or whatever it is called.
Having said all this, I generally need only very little for a 5D II file, and a very aggresive technique for a one-stop underexposed 800 iso G10 file

Kind regards, Wim

The newer Canons are clean at higher ISO. The 5D2 is awesome in that respect, even in marginal light. I wouldn't think twice about using 3200-6400 ISO with it. Lower ISOs show more noise than they did in the past on the 5D2. The 50D is clean at lower ISO (like Canon always was in the past) and does very well up to ISO 3200. Haven't shot the 7D yet...