Ok cool, now if it were my tank, I'd go with 2x6700k bulbs in the front fixture, and use 2x5000k bulbs for the rear fixture. The reason is simple, afternoon sunlight after 3pm is between 3500k and 5500k so the 5000k bulbs would work better for the afternoon. I would plug each fixture into it's own digital timer and go with this light schedule....
2x6700 come on at 9am and turn off at 1pm
2x5000 come on at 12noon and turn off at 4pm
Because the two fixtures overlap for an hour from 12noon to 1pm, this will give your tank that mid day light burst when it's really sunny out and would benefit the plants to have that 1 hour light burst. I'm sure someone will come by and debate this theory but I've found it to work great in my tanks. So the 2x6700k bulbs will give you that early day light, with the 1 hour light burst representing the mid day, and the 2x5000k giving your plants that afternoon lighting.
Although your fixtures are T5NO it will put you into the medium lighting range because they are sitting right on top of the tank.
