So, funny story about that hex pattern. The short version is, it only seems that obvious because it's in the diffusion channel, and it's actually very subtle in the renders.
I like the concept of having subtle variations between sister ships, so I got it in my head to mod Prologic9's Constitution. The as-is version represents the Enterprise, and the first variation I made was for the Endeavour, inspired by the way the Defiant appeared in "In a Mirror, Darkly" (since they're both higher-numbered ships, so it makes sense they'd both have more modern detailing). The big changes were symmetrical windows on the saucer, an aztec pattern, adding the mythical brass ring on the front of the engineering hull behind the deflector and, yes, a hex pattern on the warp engines.
I haven't needed to go through with it, yet, but I've figured I can make two more variants, based on TOS-R. The Enterprise model used for most of the run was missing several windows on the neck, which I figured would work for the ships numbered lower than 1700 (since I fanwank they were initially appropriated as older ship designs and used existing parts in construction which, I don't know, didn't have the hull strength to cope with so many windows? I haven't written it all down, yet), and a variation from the TOS-R version of "The Ultimate Computer" where two of the Constitutions seen had a bunch of extra windows, which I'd use for 1702 through 1717. Maybe the two pilot versions, too.
My source for all of this, including the screen cap I linked to, was this excellent blog post
from a site talking about modeling the TOS Enterprise in all it's forms.