the OP is just gunna get more confused the longer this thread gets, lol, its okay though, more for the OP to think about, lol.
In all honesty it looks like your gunna have to get an all new set of lenses and other gear if and when you get it for your new camera wether it be D700 or 5D Mark II.
So that gets the whole "I invested this much into this gear and now its useless" squabble.
This leaves me with a few more questions, are you going to keep a backup body to your FF camera? if so, then your probably just better off once again getting the D700 as you can keep your current D300 as your backup and remain "all Nikon".
If your not gunna be keeping a backup body and only one new FF camera, then you need to decide what your priorities for your type of shooting is:
(in your case so far based on the points you've raised)Is it faster and better AF OR megapixels. Also, consider that if you've never used an EOS camera then your gunna have a learning curve and learn a whole new camera system and how it works. In addition, consider which lens lineup do you like more : Nikon or Canon.
IMO assuming that your gunna sell your D300 I think you should pick up the 5D Mark II for reasons that a) Canon lens are cheaper b) For your purposes the 5D Mark II IMO is a better camera and c) the Canon looks better 
On the other hand if your gunna be keeping your D300 then get the D700 and stay all Nikon for the sake of compatibility and simplicity and enjoy the insane AF on the D700, lol.
Just know either way you go your getting a pretty awesome camera.