Blood tier 13 vs 12

Hi Folks.
I currently have 4 p t 13.
When should I break this?
Just got t13 chest tonight.

Thanks,
Siswai
I assume you mean 4p T12.

The 2set for T13 is quite good. I'd make the swap when you can get 2+2.
I broke it once I got the 4p from LFR. If you get 4 piece normal I would go with 2 and 2.