8/8G CM here; I went with a MS >= Haste > Crit > Vers >>>>>>>> Mastery* build and managed just fine (all my gear had MS+H or MS+C anyways). Trinkets used were Blackiron Crucible (Blackhand) and Quiescent Runestone (Imperator) as both are well overbudget and don't get scaled down appropriately.
* Mastery is really bad because ~80%+ of your DPS will be on trash. Mastery only affects your FB and FFB (and also your Welly), neither of which you'll really be casting on trash packs until the very end of them.
As for talents:
15 - Doesn't matter (used BS)
30 - Flameglow, as you want to maximize your time DPSing and not worrying about AT/wasting GCDs on Ice Barrier
45 - Doesn't matter; don't think I ever used it once, though RoF can be helpful and save a tank at times (at the cost of DPS though!)
60 - I used GI, but CS could be useful too. Removing the really nasty DoTs in those dungeons can easily save your life.
75 - This was the only real choice. I tried both non-UM talents and for the most part, they actually seemed pretty equal. I mostly stuck with IN simply because of its ease of use and consistent, non-RNG, damage. Some times with FB, I got a TON of extra damage because of some great procs! Other times, it just didn't happen.
90 - IF; could use RoP, but IF = less hassle.
100 - CmS. I absolutely loathe PC (and it's less DPS overall on trash) and TV was hit-or-miss, usually miss.
Boss rotation is pretty straightforward (if you don't know how to play Frost in non-CMs, read up on it and play the exact same way, with a bigger emphasis on not messing up fight mechanics). For trash packs (usually ~7-8 if not more mobs at a time because your tank will be pulling/chaining multiple packs), you'll want to:
1. Keep Frozen Orb on cooldown at all times
2a. Keep IN on cooldown at all times (you can hold one charge, just make sure at least one is ALWAYS on cooldown)
2b. Keep FB on your primary target, unless the trash pack is about to fully die.
3. Keep Pet Freeze on CD (as it gives 2 nice FoF procs for you to use/pop your FBomb with), but try to time it with IN casts as that will result in a big shatter/CmS or FB explosions if you picked FB instead.
4. Comet Storm, especially if it's on as few targets as possible.
5. Dump all your FoF procs (especially onto an FB target if you took FB)
6. Blizzard. (Note: There are times where Blizzard is more beneficial than using your FoF procs if you have a TON of mobs [~15+] and you picked IN over FB. If you picked FB, NEVER Blizzard over using FoF procs on a FB target!)
7. Frostbolt/FFB/IL/etc to finish off weak targets when most of the pack is already dead (make sure to Blizzard to get Frozen Orb off cooldown for the next pack though!).
For smaller packs, just remove 6. because Blizzard isn't too effective. There will be some awesome moments where you get a ton of mobs though (the 1st boss's hallway in Bloodmaul for example) and can Blizzard+Orb for days
Some tips/tricks/things that are noteworthy:
- If you have ANY melee DPS in your group, always be aware of how close your tank is to the mobs prior to using Ice Nova (if you picked it), Pet Freeze, Frost Nova (if you picked FB), or your L45 talent, as freezing mobs that are in motion towards the tank may result in the melee getting bitchsmacked!
- Pay close attention to your debuffs, as CMs drastically buff DoTs, and GIs and/or IBlocks will be needed to save the healer some mana.
- If your group is ever having trouble interrupting spells or keeping buffs off of mobs, don't forget you can spam Poly (at a DPS loss) to keep their spellcasts at a minimum or Spellsteal some buffs off. Some places where you WILL have to Spellsteal include: Hallway to/2nd boss of UBRS (Alchemist/Kyrak's healing concoction), Trash to 1st boss of Auchindoun (Void Shells and other healing/absorption effects), Anything the Geomancers/Blood Mages in Bloodmaul put Earth Shield/Blood Rage (or w/e it's called) on. (Can't remember if there were others; it's pretty late)
Hope this helps in any way, and best of luck to getting gold!