Five questions, folks. (1) I am of the understanding that the nacelles were repositioned on E-E between these two movies, but wasn't sure if they were moved forwards, or backwards, or just further out to the sides. Can anyone clarify? (2) Was there any kind of in-universe explanation as to why they were moved, i.e. to improve warp efficiency or some such technobabble? (3) Also, I am of the understanding that the reference in dialogue to "Deck 29" isn't necessarily accurate, but were additional decks indeed added to the engineering hull to change it from 24 decks to another number? (4) If the original "First Contact" and "Insurrection" Enterprise-E was 685.7 meters long x 282.0 meters wide x 75.0 meters tall, what are the stats for the "Nemesis" E-E? (5) Finally, although this question might be better answered in Trek Lit, have the more recent novels mentioned new or more elongated nacelles for the Sovereign-class in connection with being able to utilize slipstream drive? Thanks in advance, folks.
Most of these questions are too tech-oriented for me, but if by in-universe you mean canonically so, then I'm reasonably sure no explanations are provided. Regarding your last question, it's my understanding that the E-E doesn't do slipstream.
http://www.trekbbs.com/showthread.php?t=227680 A general discussion on the size of the Sovereign More generally... Ex-Astris Scientia has a good article on the Nemesis changes. http://www.ex-astris-scientia.org/articles/sovereign.htm The model doesn't actually feature any new decks and the pylon changes weren't actually given an in-universe explanation. And the Enterprise as of the end of Peaceable Kingdoms doesn't have Slipstream capability, yet, but might for the upgrades mentioned before her next mission. Also, nacelles don't really impact slipstream.
I'm of the opinion that the changes between Insurrection and Nemesis are a retcon, not an in-universe change. The reasons they exist is because it was a very minor change which made the ship look better, and that when laying out the space battles they realized the ship had a poor field of fire. There's no difference at all to the ship's length, the nacelles were just raised a bit. Lots of pics of the Nemesis CG model here: http://www.modelermagic.com/?p=2890
This blog post by John Eaves covers the evolution in quite some detail. No decks were intentionally added and the conceptual size changed only from 2248 to 2250 feet over the years. If someone could create an overlay of the various schematics, including the Fact Files orthos and the freely available Nemesis CG views, it should be easy to see how the proportions changed over time. In order to develop accurate deck plans, it would be necessary to decide which of the versions is 2248 feet long and how many of them can be rationalized as in-universe modifications.