Which 3rd prefix for a Vagan CoC weapon?

I have a CoC groundslam running GC and Blade Vortex supported by Hatred and a herald. My Vagan scepter rolled 26%crit so I can roll two prefixes. I'm thinking of:

2-5% block
0.2% cold damage leeched as life
10-19 to 13-22 flat cold damage to spells

I was originally thinking block, but about 1/2 of my GC is cold and 20% of BV is cold, so maybe leech would be better. 0.2% just sounds too low to make a difference, as does the flat damage. Anything stick out as superior?

I assume you have % spell damage on it already?

I would go spell damage.

Theoretically you could get 108% spelldamage from 2 prefixes if rolled max and ilvl is over 64 and under 80.
I dont think cold leech goint to do much for you.
The block is nice but i value spelldamage more, if im not very squish that is.

I should clarify..

Two prefixes will be:
-spell damage
-hits can't be evaded

Three suffixes will be:
-multimod
-CC
-IAS

I was hoping for a prefix with my regal, but got CC. Now I have an unexpected open prefix. I'm leaning towards cold leech to take the edge off of ele reflect. Block would be nice, but reflect is more of a problem for me now, at least until I take Vaal Pact.