I don't understand primes that aren't in the 1.4 or at least 1.8 range. Why would i want a $700 prime that is only f2? Can someone explain this to me?
Well, 1.8 is only 1/3 stop faster than 2.0. To get 1/3 of a stop out of shutter speed or ISO isn't that big a deal, so the difference doesn't matter a whole lot, IMO. 1.4 is 2/3 stop faster. Again, with the ISO performance of the modern cameras, this isn't as big a deal as it once was.
Creatively, the DOF of the faster lenses can't be replicated. But at that point you're in the realm of very carefully focused artistic shots - the realm of a more specialized lens. I have never had any luck walking around shooting at 1.4-1.8. DOF is too difficult to manage. If stuff is moving, or the scene is busy than your keeper rate goes way down. I'd much rather have the higher resolution of the new lenses and them be just fast enough to help in dim situations.
On another note: I'm guessing $1600 for the new 24-70F4 L IS.