On my Tac/Dreadnaught, I quite comfortably run five beam arrays - four on the rear, one up front, and have absolutely no issues with energy drain. Originally I tried something similar to Hakaishin, and focussed everything on forward firepower. However this meant (at least for me), after the inital Alpha strike on one target, the attack drained a lot of power and ship really wasn't that effective until the next Alpha. Even with EWP and tractor beams - people soon learn your tricks and start attacking from the side or just keep their distance and shoot from the rear. You can occasionally do some damage, but nothing people can't handle.
For example I was in a C&H a few nights back on my Eng/Assault cruiser where a Tac/Dreadnaught was attacking me for most of the match. Their setup included EWP and rear turrets. They were still easy enough to run rings around, and I just laughed the damage off. I only had two small hull heals and no Hazard Emitters - although I did appreciate their ignorable-turrets giving me free Borg procs... never got a chance to thank them for that. lol
So... beams work quite well. Yes I have lost a slight bit of forward firepower, but it's certainly not made much of a difference (in my opinion) in terms of the Alpha strikes lethality. Instead the ship still has a devastating Alpha, and can still offer decent well-rounded DPS support afterwards. I don't really have any 'blind spots' that require use of EWP or careful maneuvering to protect. Generally can keep pressure on no matter where an enemy is.
I agree though that 6-8 beams is a bit silly if you can't keep the power up. Beam boats are more feasable for Engineers thanks to them having EPS Transfer and Nadion Inversion. Probably not on a Dreadnaught though :p
Ooh, now thats a combination I'd like to try! I'd probably want it as an alternate BOff layout, kind of like the Advanced Escort and the MVAM variant, so I could choose. Not sure how much the loss of a Lt Cmdr Eng station would affect the ships survivability (especialy since the ship handles like a barge). But then again... dead things can't shoot back.
Suppose at the very least the ships gained an additional tact console on tribble.
If you remember, I mentioned that more than four beams is what taxes the ships weapons power.