More importantly, how wide is the tank (front to back)? That will give us a better idea of the usable space...
I created 3 spur/groove type formations in my 6' tank with a lump of rock on the right side. Its great.. I can move to the right about 45 degrees and see right into the clefts (grooves) in the rockwork to the back... and the fish can swim not only thru those grooves, but thru gaps between the spur rocks too... very open, without feeling like its a bunch of tumbled rocks. However, I have 30" front to back space, so there's a good reach of space to play with involved.
I'm a fan of using less rock and not creating walls. A single, very unique feature adds a huge amount to a reef... something like a big arch connecting two bommies, or a verticle pinnacle of rock, or ....
Wade