Source:

Info on crit and hit chances | 2006-08-25 09:54 | Aeus

The way WoW calculates crit rate is over ALL attacks. Crit rate is not based on hits only. In other words, if you have a 5% crit rate, that 5% chance includes misses.

A 1% increase in your crit chance does not equal a 1% increase in your damage output. This is because of the simple fact that a spell that does not hit cannot crit. If you have a 15% chance to crit but a 17% chance to miss, you will only crit with 12.45% of your shadow bolts, (15*0.83). Now add 1% crit: (16*0.83) = 13.28, or a .83% increase. Whereas 1% hit is basically a 1% linear increase in damage output.

Raid buffed, raid consumables (no world buffs): 602 spellpower

602 spellpower * 6/7 (shadowbolt spellpower coefficient) = +520.3 dmg

SB Rank 9 = (455+508)/2 = 481.5 avg dmg

481.5+520.3 = 1001.8 avg sb damage

Scenario 1k:

v1 base: 1000 shadowbolts (15% crit, 17% miss)

830 hits, 170 misses

830 * 0.15 = 124.5 crits

(830 - 124.5) * 1001.8 = 706,769.9 (damage from non-crits)

(124.5 * 1001.8) * 2 = 249,448.2 (Ruin empowered crits)

Total damage = 956,218.1 damage

v2 +1%crit: 1000 shadowbolts (16% crit, 17% miss)

830 hits, 170 misses

830 * 0.16 = 132.8 crits

(830 - 132.8) * 1001.8 = 698,455.0 (damage from non-crits)

(132.8 * 1001.8) *2 = 266,078.1 (Ruin empowered crits)

Total damage = 964,533.1

Diff = 8,315.0 = +0.87% damage increase

v3 +1%hit: 1000 shadowbolts (15% crit, 16% miss)

840 hits, 160 misses

840 * 0.15 = 126.0 crits

(840 - 126.0) * 1001.8 = 715,285.2 (damage from non-crits)

(126.0 * 1001.8) * 2 = 252,453.6 (Ruin empowered crits)

Total Damage = 967,738.8 damage

Diff = 11,520.7 = 1.20% damage increase

Conclution: +spell hit is better on EVERY LEVEL until you reach the hard cap of +16%, you will always have a 1% chance to miss

*EDIT* - Fixed math ratios for landed critical strikes

Sources:

http://forums.elitistjerks.com/forums/t ... and-mages/

http://www.wowhead.com/forums&topic=355 ... rit-w-ruin

http://www.wow-one.com/forum/topic/4630 ... /?p=357910

http://wowwiki.wikia.com/wiki/Spell_hit

http://wowwiki.wikia.com/wiki/Attack_table