if you just want gold and not realm-best times, you can get away with switching out very little. i just switch out 4 pieces of gear from my ilvl 579 heroic raid set, and then do a reforge on the whole thing (reforge costs me just 110g every time). the most efficient value you'll get is using ICD trinkets (so replace KTT with something else, like light of the cosmos from MSV) and putting 160 int gems in your CM-only gear.
you can test your CM set by doing proving grounds, which also scales gear to the same level as CM. there is a reforger inside the proving grounds but the UI will bug out if you reforge inside of it (it will show your hit goes below 15%) so zone out then back in after you reforge in there. you can also test your DPS in the endless DPS proving grounds. if you can hit wave 40 and above you are more than ready for CMs.
note that the legendary metagem doesnt work, the legendary cloak proc doesnt work, tier set bonuses dont work, and the 500 int gem doesnt work. the extra gem socket to weapon from legendary quest DOES work. the heirloom weapon from garrosh is a great weapon for CMs.
oh and play destruction for everything.
Edited by mediocregatsby, 18 February 2014 - 08:12 PM.