"Defiance - 13 wizard/6 monk/ 1 fighter."

[Phidius]

...
I'm going to TR again from wizard and im going to revert back to this same build. Except this time im going to have +6 to spell pen just from past life feats.

I'm going to get the wizard spell pen enhancements
thats +3

and im going to get the 2 spell penetration feats
for a total of +4

That means i'm going to have +13 to my spell pen as a lv 12 wizard/6 monk/ 2fighter. Just from past live, feats, and enhancements. WIll this make a notable difference?
...

I had originally planned on TR'ing my 12 wiz/6 ranger/2 monk 3 times for the free +6 Spell Pen simply for the ability to throw Waves of Exhaustion from a scroll.

13 (scroll caster level) + 6 (past life) + 3 (enhancements) + 4 (feats) + 3 (Greater Spell Pen VIII) + 1 (guild buff) + 6 (Impr. Shattermantle) = 36 + d20

While Waves is still a good debuff, I don't think it's worth the additional TR. Remember, anything worth grinding is worth nerfing.