On my 8'x2'x2' tank I am running 2 of the fx-150s one on each end along with 2 mp-40s (1 older style and 1 QD) on the back wall. I tried running a single 150 but wasn't happy with flow on the far end. Currently running both 150s in constant mode at 60 or 70%. It does push the sand around the tank especially in the middle where the 2 flows collide. The mp-40s in pulse really contribute to creating random flow as they intersect the flow from the 150s.
On a shorter deeper tank like yours I like the idea of 1 running vertically and 1 horizontally like you mentioned. That is how I plan on trying it on my new 72"x36"x26" tank once it is delivered.