I would not be afraid at all on the 5D2 to do 6400 in Av at +1/3, you just have to be a bit more careful on the 7D at 6400 with exposure, the 5D2 is a bit more forgiving. Regarding the noise removal on the 7D, I just ran my sequence of noise removal steps I came up with in Oct 09, it is a different set of steps for each color channel, but using noiseware and some of the despeckling actions in CS3.
The best thing would be to try to get into a wedding of a friend or family member and just sit to the side and test shoot a bit, in my opinion. Or even shoot during a Sunday service... I am the designated church photographer, so it may be strange for others to see me shoot during service, but it is at the church's request, so I am good with it. 
I was just a guest at these friends' wedding, so I just shot from the pews with no flash on the 7D, I didn't want to interfere with the paid photographers. I have a few 12800 shots in there too. Nothing too great really to speak of, but the bride was happy afterwards, her father died less than a year after these were taken, and she was able to download some memorable shots for her memories. I wish I had the 5D2 back then to try it out at the same time.
http://teamspeed.smugmug.com …331_Lp2vX#726360569_spuEQ![]()

