An upgrade long overdue. Would appreciate thoughts

Hello all,

Was hoping to get some advice. Let me start.

Few years ago, I used to do a lot of shooting. Worked for my school newspaper and have decent amount of experience in terms of photojournalism and sports photography. Needless to say, after school, I haven't been shooting too much. Recently, I was a second shooter at my friend's wedding and I thought the results were decent. Been thinking about going into wedding photography for awhile now, just part time on weekends (perhaps once a month?) for the fun and for the extra cash.

With that said, let's talk about the camera. I have a 20D which has served me long and well but its quite possibly time to upgrade, if I were to step into this new field. The things that matter to me most are; FF body, much better AF and ISO performance at levels of 1600 - 3200. Needless to say, a camera that would fit the bill is a Nikon D700. Not sure if making a switch to Nikon is the best idea given the lenses/accessories that I have. So if I were to stick with Canon, what would be the best option albeit a temporary solution? Perhaps a 7D, 5dmk2 or a 1dmk3/4? Or maybe, I should just rough it out with the 20D and wait for a better offering from Canon? Appreciate any of your thoughts.

My current gear, if it matters at all:
Canon 70-200 2.8 L IS
Canon 24-70 2.8 L
Sigma 15 fish