One of my reefs is a 75. I've experimented with a number of arrangements, and by far have had the best results with my current set-up.
My discharge/return pump comes out in the back center of the tank, and is fairly strong. For additional current I use 2 Maxi-Jet 600's, one on either side of the aquarium, almost in the middle of the glass, mounted about 6" down from the surface with the discharges at about a 35 degree angle toward the surface. This creates a great deal of turbulence on the surface, and blasts the return flow coming out the middle from the return pump. I have a colony of green star polyps and a bulb anenome (entacmea quadricolor) underneath the return pump and they LOVE the resulting current. For some reason it's not a constant blast either - gentle rippling and then about every 10 seconds or so there's a major undulation in the current. It's a beautiful effect! Discovered it accidentally one day while cleaning the glass.
Ideally I'd like even more current in my 75 but keep in mind your coral placement is a HUGE factor in their success. A previous post said it best - your corals will let you know when they're happy. HTH