THE source for the size of the Executor is the movies themselves. Except no substitutes.

Of course it took a PhD student to measure the scale pixel by pixel, but it was possible.

I still have no idea who would win in a battle between any given sci fi ships. Frankly the stuff out of SG-1 beats just about everything else.

Vorlon. Nothing beats Vorlon.

I think that Kosh wasn't even statted in the Babylon 5 RPG.

Vorlon. Nothing beats Vorlon.

You know, except for that time Kosh was killed.

And then after that the time that the main characters killed Kosh.

And then the time the league fleet destroyed the vorlon planet killer, saving centauri prime because the vorlons had to call in reinforcements.

Speaking of the vorlon planet killer, that is pretty clearly using the same basic technology as the Death Star. It's really kinda too bad that SW has the "long time ago..." Bit. A very strong case could be made that the B5 universe develops into the SW universe over several thousands of years.