WotLK Spellpenetration

taken from my guide:

Short thing about spell penetration: Spell pen is good since it lets you ignore resistances. With this your chimera shot, serpent sting, explo- and immolation trap, arcane shot, volley do full damg on targets with fire/arcane/nature resistance. I strongly suggest having a second pvp weapon. One with for example 2 resilience gems in it, the other one with 2 spell penetration gems in it. Preferably the jewelcrafting ones that grant 43 spell pen per gem (86 in total). With this you can swap to spell penetration when facing a mage (80 resilience over talents. Possibly 40 additionally from mage armour), druid (mark of the wild on the whole teams grants 75 resistance) lock (felhunter has like 160 (???) resistance) teams. If you know u are gonna face for example a good mage team (mage has mage armour as well = 120 resi) or a lock team where your major goal is to kill the lock pet, you can enchant 35 spell pen on your second back, put a 43 spell pen gem into it (with the 264 pve back from badges you activate +4agi gem bonus) and put a normal 20 agi gem + your second 43 spell pen gem in your third pvp wep. With this geming and gearing strat you gain 121 spell pen (perfect for mages with mage armour and definetly better against lock teams where u kill pets) + 2 gem bonuses you would normaly not obtain.)