I first want to say that my advice is only a suggestion and not definitive. I have learned that some peoples ideas of flow don't agree with mine. Growing up near the cost and near rivers I know natural bodies of water have a tremendous amount of flow energy, the few little powerheads most hobbyist use are not equivalent to this. I also don't use or believe in DSB's so I have no personal experience with this latest trend. I am old fashioned and generally avoid fads- 2" of aragonite sand of 2 to 3mm generally is what I use.
The ideal is to have one pump on each side. I have a 4ft 120gallon aquarium and I use 2 7400/2 Turbelle on a 7094 multicontroller. This has suited me quite well and I attach a photo. My return from the sump adds about 500gph to this 2100gph of flow giving me a 20+ turnover rate. My friend Bruce Kelley uses 2 2002 and a 6080 Stream on his 125- 6ft aquarium. The 2002 are pulsing throught the use of a 7082 controller. The 6080 creates a static length wise flow. Bruce always uses a plenum. Return flow is about 500gph. His total flow is about 4000gph. He keeps almost exclusively SPS though. He noted some damage to a Montipora capricornus after first adding the Stream. Realisticaly caps grow near the surface in seas that at the roughest in storms would pulverize a human being against the rocks so I can't imagine that it is too much flow and the corals did fully adapt- just wanted to through that in because a few people have said the pumps are too much and damaged their coral- only because they are used to poor flow. My friend Aaaron Strong uses 2 6100's on a 7094 controller in a 180gallon 6ft reef tank. He uses a DSB and also has patches of mircle mud. His tank is a real show stopper of almost all SPS and a very natural patch work of LPS, polyps, mushrooms, and clams. At first the 1 6100 he started with was to much and stirred the sand but as the sand bed matured this stopped and he added a second one.
My advice is to try to find a hobbyist with some Tunze pumps that you can visit personally. Barring this I would probably suggest 2 7400/2 or 2 6000 Streams on a Multicontroller 7094. The Streams do require patience- we are about 4-6weeks behind.