As such the borg seem way too powerful, due to their techs. In fact, to kill them there is only one AI that can do it : the rage. Kill the Borg before they reach the nasty borg tech levels, cripple them before they achieve mega-evil status. Most of the Rage's ship bear a self destruct device, so I don't remember seing a taken warship in the borg's fleets. And I have not seem them attacking a planet without glassing it either. I would suggest to have also a borg AI Version special TDM (no new techs).
I welcome them for a more interesting solo game. I think it would be interesting to cross them with deathstalker's hell mod, to avoid the problem of my cheap and well trained destroyers wipping out entire fleets of AI dreadnoughts.
I'll give it a run.
I did enjoy a lot of fun looking at all these aliens bLasting themselves !!