Plasma cannon is really interesting weapon but in the current version they dont seem all that great....after the patch that surely could change but im afraid they might end up being dead weight like the Tach Lance.....anyone here using Tach Lance?
Both my Paragons have Tachyon Lances in the large turret slots. They can already take on any other capital ship, so throwing on the Tachyon Lances gives them some ability as fire support. Since it takes so long for a Paragon to get into battle, this lets them be useful sooner. They're also really good at taking out fighters (and Hounds) and can cripple a frigate or destroyer if it manages to catch one with its shields facing the wrong way. They also pretty much hard-counter phase ships, though the HIL has it beaten in that regard. Tachyon Lances are also really good at disabling all the weapons on enemy capital ships, which can drastically reduce incoming damage.
The Tachyon Lance may have high flux requirements and it's damage/flux ratio is, I believe, the worst in the game, but it provides such good utility to a fleet that it's still worthwhile. I'm thinking of stacking a fleet with Lances, since I haven't actually tried that strategy since the nerf. I think it could still be effective, but I need to do some Science on it to be sure.
There are designs for the Paragon without Tachyon Lances that are better at fighting other capital ships, but they drastically limit their usefulness against anything smaller than a cruiser- it takes forever for a Paragon to get into battle. Besides, a Paragon can already beat any other capital ship; giving it a Tachyon Lance doesn't make noticeably worse 1v1 and gives it some uses aside from winning a slugfest.