The optimal number of beams depends completely on your Weapons Power available, (which, at the same time, depends on your class Abilities, Starship, Boffs skills, etc...)
- At less than 100 Weapon Power, stick to 4 beams maximum.
- If you have about 100 Weapon Power, 4 beams are optimum, 5 will do a bit more damage than 4 (but maybe less than 4 + 1 torp/mine launcher properly managed), and 6 do exacly the same damage overall than 5, (wasting that sixth slot). 7 and more are in fact a direct loss of DPS.
- If you can reach almost constant 125 Weapons Power, 6 beams are optimum, and even a 7th one will slightly increase your damage (albeit less than using a good Torp Tube or Mines, even if not specced for them).
As I answered on the "Beginners Guide to Ship's Power 2.0" thread in this same forum, I've tested several times succesfully that having more than 125 Weapons Power available (with Emergency Power to Weapons for example or EPS Power Transfer engy ability), does indeed improve the DPS when firing multiple beams, even when max WP is capped to 125 (donīt believe what some others may say, better is to try and test it by yourself).
7-8 beamer ships should only be worthwhile on setups with high base Weapon Power and with a constant rotation of EPtW, and using Nadion Inversion on every CD available.