[Buldooser]

Hi, I have followed this guide : Cider's Easy 540 Defense Gear Guide
and have got my 543 defense rating now, I have been running some heroics quite some time now, but only the ones I knew I wanted something from.
So I would like to know which items should I start switching now and move on to?
Any ideas and help will be much appreciated.
Also I would like to know what kind of stats do I need to go to Naxxramas as an off-tank.. Our guild has pretty good tanks but I think I could go as a dps too, but since I am stacking tank gear I would prefer to go as a tank, since my dps as arms is not very high(mostly my guild let's people roll for off spec too, I think. At least when they are timerunning).
So I am asking what kind of HCs should I be doing now to get what kind of set? (a set would be very much aprreciated also).
Thanks!
By the way I looked into some of the guides included in the guide but they didn't seem to have much of an upgrades, but aren't my stats a bit too low for Naxx?
Also my armory hasn't quite caught up with me so my Band of Frosted Throns has now been replaced by Unsmashable Heavy Band, which brings me to 543 defense.