I found this chart (on WoWiki, I believe...posting from a different computer so can't check).
Quote:
76 hit is the cap with 5/5 Shadow Focus
101 hit before you can go to 4/5 Shadow Focus
126 hit before you can go to 3/5 Shadow Focus
152 hit before you can go to 2/5 Shadow Focus
177 hit before you can go to 1/5 Shadow Focus
202 hit before you can go to 0/5 Shadow Focus
All numbers rounded up to the next whole number.
1% hit = 12.6 hit rating at level 70.
* Spell hit increases the chance spells will hit
* Base chance to hit is based on level difference
o 96% chance to hit an even level target
o 83% chance to hit mobs 3 levels higher
o 87% chance to hit players 3 levels higher
o Chance to hit caps at 99%
* 12.6 spell hit rating per 1% spell hit at level 70
o 202 spell hit rating (16%) needed to hit the 99% cap against raid bosses
*edit*
Of course the above table will be obsolete when the new talents are introduced in the upcoming 3.0 patch. MMO Champion has a talent calculator.
http://talent.mmo-champion.com/?priest=
Of course,the patch is still being tested on the PTR so things may change in a few weeks.
One small suggestion that you can use or disregard:
If you plan on keeping 5/5 shadow focus, you may wish to replace spell hit gems as you are over the hit cap. You should also consider replacing your spell damage/spell penetration gem (on your pants). Spell penetration is useless in PvE..it is purely a PvP stat.
I found some articles (as I changed computers, heh heh) so you may check them out if you wish.
http://www.wowwiki.com/Spell_penetration
http://www.wowwiki.com/Spell_hit_rating
This isn't quite related but is good reading also:
http://elitistjerks.com/f31/t16977-shadow_priest_101_how_melt_faces_effectively/
Edited, Sep 25th 2008 2:43pm by Miskreant