As a caster class, how important is softcapping spell penetration?

[mercutiouk]

Just curious as i've only recently noticed I was about 100 spellpen under the softcap. Will I be expecting awesome gains in DPS for getting cap?

For randoms coming from the front page - PVP forum

[worsthitmanNa]

for shadow priest its important ur fear or horrors can be resisted which sucks same for mind control. i know locks fears can be resisted deep freeze probably resistable.

[Deleted]

Get the soft cap, no excuses. Just buy the cloak and smack the enchant on it. You want fear to resist? Nope, You want that MB crit to resist? Could easily mean the difference between life and death.

[Imgrac]

Even as a just above average BG PvP'er I always go for my spell penetration cap first, in my eyes the more time I am resisting the more time the enemy has a nuking me down or forcing me to pop my defensive abilities prematurely.