Sadly, I don't think this piece of armor is best for anything at all, at least I didn't find where it would shine. I also have it and never use it.
I theorycrafted it should make travincal sorc pretty awesome with high blizzard damage, but it turned out that I didn't find ANY difference between having 14k and 10k damage on her, only thing Ormus did to me is made me more vulnerable and easier to get killed. So, even for Travincal this armor is simply outperformed by a simple Vipermagi or more optimal choices in 1.07 Ark or CoH. Even without Ormus it is possible to get near 12k damage if one chose to do, so it is almost like a waste of slot pretty much.
In MF environment, this armor sucks. Better and much stronger alternatives are 3 piece Tal's set (amulet, armor and belt) or Skullder's or even Enigma all crush Ormus into pieces. For general play, 1.07 Ark is really great armor to have, I used it on CS sorc who is fastest leveling character in diablo world up to level 97 (or maybe even 98).
Long story short, blizzard ormus is one of those armors that looks great, but offers little to nothing compared to alternatives. Only potential use of such armor I see is in PvP where you can achieve potential 4k+ instakill damage while being really glass cannon yourself. Other than that... not really impressive piece of equipment.
When to respec to MF? When you are ready to nail some AT running, no sorc is better than AT blizzard sorc for MF.