Now that I think about it some more, I'm beginning to lean toward the dome above the bridge. They've already established the bridge is three or so decks down. And the corridor behind Kirk probably isn't as long as it seems (wide-angle lens). It would fit in the short segment just under the dome, ending at the vertical slats / windows (seen for example here: http://www.ncc1701shipyard.com/image...es/burning.jpg
So, I'm going with "above bridge" dome. Which makes the Enterprise about 350m long.
Exactly what/where I'm thinking.