You took me seriesly! :) But OK--
I view the Star Destroyer as having the mass and maneuver characteristics of a Borg Cube, and therefore the dynamic of the battle would resemble that between the Cube and several starships including Enterprise at the beginning of "First Contact". The large number of turret-mounted particle-beam weapon on the SD might provide an initial advantage, but if the shields could be disabled (by destroying the exposed shield generator) the turrets could be shot off.
If Easy Company were dug in on Balaclava Heights, the battle would have gone no better for the Light Brigade, IMHO. The rapid-fire, highly accurate weapons of the WW2 era would have made up for the smaller force.
I agree with you re the Romans and Greeks.
As for the sea battle, what would you make of the advantage in speed and maneuver provided by the steam engines? Would Captain Aubrey's "weather gage" be rendered irrelevant? Were any Spanish guns of 1588 capable of penetrating either the armor or the water (if aiming below the waterline)? I don't know.

See y'all Friday...unless I find a cyber-cafe or sumpin'*
*Not likely, as we plan to stay in woods and trails
Is there a video game where you can have fantasy historical/sf battles like this? If not there should be! :)
You're probably right on the Star Destroyer and Easy Company scenarios. On the Armada vs. ironclads, I was thinking the steam engines' manueverability would be nullified by the fact that the ironclads would be surrounded. I'm assuming at least some of the Armada's guns could penetrate the ironclads (some of the Armada's 130 ships had better guns than others), since cannonballs were initially designed as seige weapons to blast through stone fortresses, and since there are cannonball dents in what remains of the ironclads (there's a museum online with some pics); but I can't claim to know that for sure. As far as penetrating below water level, I was thinking the most feasible way to do that would be via ramming rather than cannonball.
Have a good trip!