Well I'll comment on your two ideas.
1) I'd change one of the elemental shamans to resto. It's hard to keep up on heals these days, especially when you need to stop all 3 from DPSing to heal your tank (or each other in a Poison Nova kind of event) plus they go out of mana so quickly. But a resto shaman can DPS in between riptide etc. like no big deal. Plus that way you've got a pally who can dispel poison/disease, a mage who can dispel curses, and a resto shaman who can dispel curses as well as magic.
From my experience running with an Arcane mage in the group, I have to say I'm quite happy. They're boring to single-box. Their highest DPS is firing off a few arcane blasts in a row (because each one buffs the next up to 4, but makes it cost more mana). You can't just do arcane blast because they start costing a few thousand mana per cast when they're up to 4 stacks, so you want to mix something else in. Either arcane bolt or the arcane missiles proc.
I just leave arcane missiles on another key (it's my AoE key for the tank, consecration etc) so when it's up I hit it. That way the mage keeps the cannons firing without having any mana problems.
Straight out of the box as a new 80, the mage's DPS was beating 2 of the group already (and they were in tier 10 gear while the mage was in i187-i200 gear)

2nd group option: Blood DK is meh. If you like it you like it. I preferred the frost days. Blizzard seems to love them though, so go for it if you like playing them. I just don't. There's a lack of Crusader's Aura and buffs here.
Disc Priest has cure disease and double dispel magic. Yay! I don't know how good or bad their group heals are, but people say they're better raid healers than holy priests. Plus they have damage mitigation for everyone.
The boomkin can remove curses and poison. So between the druid and priest you already have your dispels covered.
Arcane mage is the same as before. But I forgot to mention portals.
Affliction lock has the problem of their DPS looking small, but really it's because they're laying on DoTs that won't ever fully blossom into the springtime of affliction they're meant to be. But they're always good for summons eh?