I have a teriffic idea about the ISD size and lag problem. In the book... Darksaber, I believe, there are smaller 'Victory' class ISDs. Ah! I found the book... here is the quote:

"...she recognized the fleeting forms of seventy-treee Victory-class Star Destroyers, smaller warships each about half the size of an Imperial Star Destroyer. But these ships were fast, agile, and bristling with weaponry. Their hulls were made of a crimson alloy so that the Victory ships looked like bloody fangs clamping around Harrsk's Star Destroyers."

I personally have no modding ability, but it sounds like this would be an easier project than a regular ISD, and I would love to see one flying around.