Brand DOES NOT MATTER (at least not much). I'd go for 2x8GB if using CAD tools, and CL9, DDR3-1600, 1.5V.
Please elaborate a little more. How is it that you know brand does not matter, and why do you suggest that quantity? I am looking for reasoning with the advice so that i can hopefully make an informed decision.
All the brands use much the same manufacturers (very few are OEMs) - exactly who soldered them to the PCBs and who made the actual chips doesn't change much. The only real difference is binning, default rates, the heat spreaders, and branding.
If using cad tools you may want 16GB - not certain, up to you.
Getting any faster (lower number) than CAS Latency 9 (CL9) increases price significantly without doing much to the speed. Same for going above DDR3-1600.
Using more than 1.5V RAM is dangerous to Intel's IMCs (Integrated Memory Controllers), and voids your warranty.