Which piece was the best was more or less what piece had the highest item level, as there was normally only one spell DPS 372 item for each slot currently discovered.
helm - Crown of the Twilight Queen - http://cata.wowhead.com/item=60237
neck - Valiona's Medallion (heroic) - http://cata.wowhead.com/item=65112
shoulder - Firelord's Mantle (heroic) - http://cata.wowhead.com/item=65213
cloak - Shroud of Endless Grief (heroic) - http://cata.wowhead.com/item=60232
chest - Firelord's Robes (heroic) - http://cata.wowhead.com/item=65212
bracers - Bracers of the Bronze Flight (heroic) - http://cata.wowhead.com/item=65138
gloves - Firelord's Gloves (heroic) - http://cata.wowhead.com/item=65209
belt - Belt of Arcane Storms (heroic) - http://cata.wowhead.com/item=65034
leggings - Firelord's Leggings (heroic) - http://cata.wowhead.com/item=65211
feet - Einhorn's Galoshes (heroic) - http://cata.wowhead.com/item=65069
ring1 - Signet of the Fifth Circle (heroic) - http://cata.wowhead.com/item=65123
ring2 - Signet of the Fifth Circle - http://cata.wowhead.com/item=59501
trinket1 - Theralion's Mirror (heroic) - http://cata.wowhead.com/item=65105
trinket2 - Stump of Time - http://cata.wowhead.com/item=62465
mainhand - Blade of the Witching Hour (heroic) - http://cata.wowhead.com/item=65091
offhand - Book of Binding Will (heroic) - http://cata.wowhead.com/item=65133
wand - Theresa's Booklight (heroic) - http://cata.wowhead.com/item=65016
There were a couple items (mainhand, trinket2) which had a few possible items, and I just kind of picked one (trinket2 I made a hit trinket, maybe not the best choice, but a good one)
The mastery(m), haste(h) and crit(c) rating totals are as follows, enchants unincluded, many enchants are int, anyways.
m = 1262
h = 1942 + 80(4 sockets) = 2022
c = 1106
After reforging your robe, [boots or belt], ring1, ring2 and cloak from haste to hit, you are 3 hit over the hit cap, I couldn't find a way to make it closer.
This means that your final numbers are
hit = 1744 = 17.03%
mastery = 1262 = 7.04
haste = 1201 = 9.38%
crit = 1106 = 6.17%
Pretty low numbers, lower than I figured for the first tier of raiding.