My guild has been farming Hodir on Hard Mode for the past 3 weeks (still haven't gotten the achievement though for some reason), and there are several things we found that greatly increase the raids' DPS.
First and foremost we have everyone in our raid enable Projected Textures in their Video -> Effects options, this allows the normal icicles dropping from snowflakes to display a blizzard rune circle on the ground covering the affected area. To maximize DPS we just step outside of the circle a couple seconds after it appears and wait for the icicle to fall then move back into the Moonbeam, obviously preferring Moonbeams near a Fire.
For tanking position, we have our tank have his back against the cache to the left when you enter the room, putting Hodir in the corner. This forces the NPCs to be closer to him and the Moonbeams and Fires are all spawned in a crescent within 20 yards of Hodir. Players are all closer together within the crescent, allowing less movement with Stormclouds and Flash Freezes. With Stormclouds we force that one player (who is marked with a skull from DBM) to spread it to as many DPS as he can, the first Stormcloud attempting to get it to the tank to minimize threat issues. Having one person moving to spread it is better than the entire raid moving to him, in terms of DPS. Obviously everyone focuses on Flash Freezes to break out NPCs when they're trapped as priority over the boss.
So far with this setup we've killed him in an average of 2 mins 35 seconds, this week being 2 mins 55 because our mages forgot that our locks don't provide 5% crit with their fire-destro build, and didn't apply scorch. Last night we brought a caster-stacked group for 10 man and killed him in 1 min 38 seconds
As far as what I do for the fight myself, I have a crit set pushing 800 crit rating with only sacrificing a minimal amount of Spellpower and a lot of Haste. Since most of your DPS is going to be during Moonbeams and when you have the crit buff, stacking Crit to get a Lunar Eclipse ASAP with it will yield more than stacking haste like our usual setup and almost pushing the GCD cap with Starfire. Movement-wise you obviously want to minimize it as much as possible to maximize your DPS, I only apply my DoTs when I do have to move. I typically push around 13k DPS, 15k being my best on kill.
Just some helpful tips to maximize you and your raids' DPS :]