I primarily tank as Blood. I love my Blood Spec, but I've been debating about changing up with Frost for a change of scenery. IMO, I feel that Blood is the best for survivability, but that is open for debate, but I'm not here to discuss that.
What I am looking for, is if Frost Dual Wield Tanking is viable. I know Frost Dual Wield is viable and I Definitely wouldn't mind looking into a dps type build once I get my dps items built up, but I'm more looking for that tank spec if possible.
To be honest, I haven't tanked on my DK yet, frost, DW or otherwise. Mostly because I'm still leveling it and want to get stuck into the cobalt crafted gear before I do. So sadly, I'm not a lot of help to you there. I imagine you can get defensive 1 handers that will give you some more avoidance than you would from brutal 2 handers death knights usually use.
I'm not sure how parry haste etc would factor in to DW tanking.
I've just recently lvled my dk to 80 and i'm using a dual wield tanking spec - frost.
I'm currently on the progress of getting gear so i can't have an 'endgame' approach. Although, i can say one thing.. i ENJOY it - ALOT! Dual wield tanking is loads of fun, i've had a paladin tank etc in the past but it's just like a rogue tank imo. Maybe the mechanics tell us that it's not as viable as other tanking specs with 2h's but like anything else, if you stick with it - you'll get used to it and you'll in turn, become good with it!
Give it a go, the gems aren't dramatically different that you use, so i mean a change would maybe cost you about 1-2k max from DW to 2H.. imo
To my knowledge the parry haste is very prevalent in say ToC, but in ICC most bosses don't do it. (quick google reading would say that only Deathwhisper and Sindragosa have parry haste - so don't DW tank them)