Interesting Info on Elemental Resist Reduct and Penetration

Im making an ice witch and toying with the idea of both the Elemental Weakness Curse and Cold Penetration Support Skill Gem.

After having done some research on how they work it would seem great for anything that isn't overcapped on resistances for example:

something has max resist but not overcapped - 75% and i have both level 19 skill gems so 38% lowered resistance on EW and 34% penetration on Cold Pen it would then apparently be:

(lowered resistance gets accounted for first, and can't lower the max resist if an enemy is overcapped, whereas penetration is factored in second but lowers by the actual current resist even if overcapped, and if enemies have low resists they can and will go into the negatives not stop at 0)

75% - 38% EW = 37% - 34% Cold Pen = 3% Cold Resist Left

150% (75% cap) would be 150% - 38% EW = 112% (still the 75% cap so no effect whatsoever) - 34% Cold Pen
= (apparently the cap gets pen'd, not anything over so 75% - the 34%) 41% resistance left.

Source: http://pathofexile.gamepedia.com/Penetration

So if i have understood the above source right, Ele Weak can potentially either reduce less of a resist than what it shows, or none of it if overcapped high enough and i guess it would be the same for frostbite and any other resist lowers as opposed to resist pen.

So resist pen reducing from the cap, not whats overcapped op and resist reduction potentially weak to completely useless in some situations?

Discuss.

I think you'll find that it's much better to have a secondary effect rather than a duplicate effect. You'll get more mileage out of a curse like temp chains than one that just makes your damage higher. I'd look to filling a weakness in your character before building on its strength.