Which stat is more important/bigger affect on fractured winter glass, cdr or + conjuration skill? I managed to get my hand on a winterglass with 0.2 cdr and + 6 ga conjuration mastery. Is there a huge difference between 0.2/0.3 cdr?

I would prioritize the conjuration skill. 100%. I have zero issues with cooldowns.

Dont think its about the actual cooldowns but when ur conjuration cooldowns are reset /shorter in lightning spear you are actually doing way more damage is what I heard

Mastery > cd's ofcourse

+2 mastery is 2% damage for each active conjuration. You have around 15-40 of them up at a time so that's 30-80% more damage.