as a life long Trekkie (I'm 21 and my uncle raised me on TOS) I have no problem with the new Enterprise being 700m long. My whole take on the thing is (as if i matter) that when the Kelvin encountered Nero's ship, Starfleet was like holy crap if the romulans, earths #1 rivals, have ships that huge and powerful we need to do some major rethinking on our ship design, hence the giant redesign of the constitution-class and the others we saw on screen, also would explain why the enterprise was not launch until 2258 instead of 2245, Starfleet needed the extra years to design the constitution because it is so big