Sk/clr/bard/ber/ber/ber is better dps than the mage/caster setup, though the mage setup is definitely good dps overall. Wiz in place of mage is a tiny bit more dps, but zerkers can still outpace wizards.
Swapping a Bst for one Berserker (Tank/Heal/Brd/Bst/Ber/Ber) is a favorite group for a lot of mutliboxxers. 3xBer does open up Alliance which is insane DPS, but it is very endurance intensive. If you're just alliance'n on Named it's great, but if you plan to run it 24/7 I'm not sure Breather disc + Bard will keep you going.
Bst/Bard is a great endurance regen setup, plus gives you watered down shaman buffs.
The real strength of this group is "haste v4", or weapon delay reduction. You get a few Ber AA/disc's that do this, but Bst's Dico Rage is -33% WepDly reduction for almost half of every fight at 26 second buff on 60 second recast. Bard's Quick Time is -15% WepDly for 4 minutes too (10 min timer.)
Really either group would do fine in 95% of RoS content. Daybreak tossed in a few named/events that favor melee or caster DPS, but you can usually work your way through them even if your group isn't ideal.