-*Freezing Pulse 6L, what gems to sock with?*-

So im using Kripp's spec, so im gonna be using Blood Magic and ofc Freezing Pulse/GMP/Life leech

Blood Magic
Freezing Pulse
GMP
Life leech

2Spot left, what to use?
Faster casting
Added cold
Added light
Added chaos
Cold pen

Currently tried added light/cold and Faster casting
Added cold is nearly a most in my opinion.

So 1spot left?
what to use?

Faster Casting for sure. You have Life Leech and Blood Magic, so more casts = more DPS and Freezes and you will leech the life back anyway.

If you are using Kripp's spec, then you will have a curse for additional Cold Damage (usually Frostbite), heck you could even go Critical Weakness and benefit more from Shattering (not sure if you have all the crit nodes yet, but when you get them you should have around 25+ crit chance, and with GMP its very useful) so its really unnecessary to get Cold Penetration.

Added Chaos is useful as an additional damage increase over Added Cold, although the the differences can be negligible if your Crit Chance is decent (20+).

Added lightning is an interesting one, http://www.reddit.com/r/pathofexile/comments/18ebtl/analysis_of_shocked_in_kripparrians_build/
Suggests that its unnecessary, but some users say that it can be useful (Kripp also tested this as well, and gives his opinions on it on Twitch).

good luck farming it up :D and mind the Lightning Thorns on those Mages.