Assertion 1: Executor shares a common bridge tower design with the standard Imperator-class.
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Assertion 2: Given the above, we can determine Executor's overall length. The preceding image is extracted directly out of this composite (the only difference is that I changed the background to blue in the composite 'cause the gray was messing with my head).
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Click the image for a 6000x1000 pixel version, if desired
I composited these together from multiple photographs of the studio models to present the most accurate possible "orthographic" side view of the Executor studio model without resorting to a second-tier drawing of any kind (which tend to be inaccurate). The images were taken from those listed in the Executor exhibition section of the SWTC. The Star Destroyer composite is from the Cloudster model gallery of that ship. Bear in mind that discrepancies in the line-up exist for the simple reason that the photographs were taken very close to the model for the sake of capturing detail, when they would ideally be taken from far away with a zoom lens to "flatten" the image. Such is the problem with composite imagery, but the overall size is more or less accurate.
Important: The Executor composite is incomplete: there's a bit missing from the bow, which is why it doesn't end up being exactly 11 miles long. The photo was simply not available to finish the composite, sadly.
This discussion should not be considered open for debate (despite the fact that EU minimalists and Saxton-haters seem to think it is). The above evidence is airtight conclusive and arguing with it demonstrates your stupidity. It is directly derived from G-level canon. Deal with it.