Measured on a one-minute single-boss fight in points of Spell damage: 1 % spell hit 14.4, 1 % crit 8.79, 1 % casting speed 2.22, one Nature damage 0.82 and one Intellect 0.77. Each comes from the benchmark set, so it prices a little more of that stat from where this gear stands.
Per point
- Spell damage1.00
- Nature damage0.82
- Intellect0.77
- Fire damage0.16
- Mana per 5 s0.05
Per 1 %
- Spell hit14.4
- Spell crit8.79
- Casting speed2.22
Hit
Before hit, one spell in six misses a raid boss (17 %, Classic's figure, kept by our simulator), and 1 % misses whatever you wear, so hit stops helping at 16 %. The Stormcaller has no talent for it, and this set has 4.0 %, all from gear. That leaves you far below the cap, which is why hit leads the list on every fight. A Tauren's Endurance adds 1 %.
Crit
Your spells crit for 190 % with 
Elemental Fury at 4/5, so each 1 % crit adds 0.9 % of a spell's normal hit to its average. The simulator's sheet shows 17.6 %, but 
Thundering Strikes adds 5 points to every spell and 
Call of Thunder 3 more to your bolts, and neither appears on it. Crit has no cap that matters here.
Casting speed
On one boss for three minutes, 1 % casting speed is worth more than 1 % crit, since it fits more bolts into the same time. Against three bosses for two or three minutes it falls to 1.31, because mana is the limit there and casting faster only empties the bar sooner. On the one-minute fight it also measures low, 2.22, for a reason we haven't found, so on short fights spend your stat budget elsewhere.
Intellect and spell damage
Each Intellect point is 15 mana and a sixtieth of a percent of crit, and 
Mental Quickness adds 0.3 spell damage to it. 
Ancestral Knowledge and Blessing of Kings raise each point you wear by about a fifth before that. When mana runs short, Intellect climbs to 1.04 on three bosses for three minutes, against 0.66 on one.
Nature damage counts for Lightning Bolt and Chain Lightning only, about four fifths of your damage on one boss. Fire damage, worth 0.16, reaches only Flame Shock and your totems.
Mana regeneration
Spirit is worth nothing: you cast all fight, and without Restoration's Mindfulness no Spirit regeneration continues while you cast. MP5 always counts, but on one boss it barely registers. On three bosses for three minutes it is worth 0.83 a point.
On every fight
Spell hit tops the table on all six fights. Against one boss crit and casting speed come next. Against three bosses for two or three minutes Intellect and MP5 rise, since mana decides how many top-rank bolts you get.