I use 2x 6000mah, and get about 12 minutes (Z15 for NEX). Actually, the other night I got 17 minutes, but that was doing super light flying... hovering and some light left/right, fwd/back, yaw testing.
As for EVO, I would have agreed with BK, but true, with new motors/ESC/props, it will probably change... to what extent, who knows.