Considering I had 4 DBBs on my excelsior and played that build in PVP as well it still doesn't do half way damage as when I equip 8 Beam arrays. I've had several builds with my excelsior but non was better than having Full Beam arrays equipped.
I dont run only beams,
Phaser DBB Mk XI (VR) x3
Quantum Torpedo Mk XI (VR) x1
Phaser Beam Array MK XI (VR) x3
Quantum Torpedo Torpedo Mk XI (VR) x1
This setup does just fine for me DPS-wise. The power drop is tolerable, and the Quatums add to hull damage nicely. I give up a small blind spot in the front on each side, but honestly, I've never had a time where it mattered. I used to do the 8 Array tactic along time ago, the power drain is too much and it is kind of boring to me.