Help with a PSU and Case

I would go with antec on this one, the fan will barely run so it wont affect the air flow much which is what cooler master is concerned about as the fan is an intake and would disrupt the hot air rising to exhaust fans mentality. Most antec cases have bottom mounted PSUs so i think its pretty safe to assume that even having the fan sucking in on the bottom, with a good efficient PSU, wont need to draw very much air in so it wont affect airflow much.

You have the PSU airflow backwards, it would be pulling cold air from the bottom and blowing it out the back if it were facing down. Thats ideal conditions for cooling a PSU if there is enough dust free clearance below. The storm scout has a grill there to give you that option, many bottom mount PSU cases require modding to do it (like antecs).

In antec cases the PSU pulling air from the central chamber and out the back creates airflow that helps pull the cold air from the front and side vents to the GPU without the optional side fan mounted. The GPU almost divides the case into a dual flow system with one front fan send air to the CPU and out the back/top and the other pushing air to the PSU and GPU then out the back.

By experimenting with different fan locations and speeds you may find some airflow setups help you cool different components better than others. On the storm scout that would include trying the PSU in both facings.

With 2 GPUs you may want to put an optional side fan on to blow cold air from the side grill straight to the GPUs and then face the PSU fan down to pull cold air from below. You should also consider adding an optional fan to the top to blow the hot air up and out faster.