i am on the same boat, i can't afford F2.8 zooms, so the F4 series 70-200 is what making me stay.
but for those who don't buy 2nd hand body, the D600 sounds like a pressure to Canon indeed.
I am sure if Canon simply drop the price on the 5D2, loyal Canon fans will stay. some people may never want more than 9 pt AF system and will satisfy with an old but still decent metering system.
Competition is always good, we should hope for other manufacture to pressure Canon more as well, at the end, it will benefit the end user.