Gravitational Turrets go up by 2k knowledge per upgrade level whereas all other turrets (except the short range turret) go up by 1k per upgrade level.
Counter-Negative-Energy turrets: Not sure how much use they get for people who play with astro trains on, but I know I never use them since they only really counter munitions booster (a special ship) and starships (can't be stopped by tachyon beams so they won't stay within range). Might be worth dropping their knowledge cost to 500 since they're in that odd set of things like advanced warp sensors to me.
Not that I actually know what the counter-negative-energy turret's range is since unlike other defensive turrets (tachyon, gravitiational, tractor) I don't know what it's range is since it's special-ability note doesn't say.
Tachyon Beam Emitter Normal/Stealth should be in the "Turret" tab, not the "defense" tab, since they're almost always used in an offensive-defensive manner like the tractor beams and gravitational turrets, not in a defensive-defensive manner like the shields, or mines, or repairers or whatever. Plus it means you don't have to continually keep swapping tabs when building wormhole defenses.
Increase with power cost isn't divided intuitively across the offensive/defensive turret groups. All offensive turrets are a fixed cost, except the lightning turret, and all the defensive turrets have a variable cost per upgrade.
Lightning Turrets III are considerably worse value then Lighting Turret II due to the increase in power cost per level, but not increasing the same linearly in damage per level, unlike the other turrets who's MkIII's are "less valueable" but not remotely to that extreme.
For that matter Laser Turret's I, II and III all cost identical metal/crystal. This was probably unintended.
Hrm... I think that's all.
