Deepreef, you never said what you want to keep in the tank. Livestock will dictate pump and flow requirements. A softy tank would need way less flow than a LPSdominated tank, than an SPS dominated tank. Say you are setting up a SPS dominated tank starting with frags, then any of your options you listed would work and be way more than enough right now on a young tank 5ft long. However, if everything goes well and your SPS frags grow into full size colonies in 2+ yrs, that's where your question about enough flow will warrant more consideration. As the corals grow, especially stag type branching growth, the corals themselves severely limit the flow and that is why you hear people saying they need more flow. I started my current 90g peninsula 2 yrs ago and I put 2 WAV pumps in. If I turned them up anything over about 25% I would create a major sandstorm. Fast forward 2 yrs and my tank is nearing maturity in terms of SPS coral growth. I have to prune my SPS corals or they will touch the glass or magnet cleaner in many places and almost all corals are full grown colonies. Now I still have my same 2 WAV pumps but now even at 100% I can no longer create the sandstorm. I have them set at 80% now for daily flow and I'm thinking about adding more flow.
So in my opinion for you setting up a new tank, get what gives you a nice base flow and realize that as the tank grows you will need your pumps capabilities to grow with it. Also keep in mind that there certainly can be too much flow initially. As my tank has grown, I've increased the flow but the SPS colonies near the pumps actually see tissue death crated by too much flow near the jet of the pump. So make sure whatever you buy today can be turned down to the needs of today but can also be increased for your future needs if they increase. I also think multiple smaller pumps is better than 1 big pump because you can direct them and control the output so much better.
Also thought I would mention I have a 2nd 46 gal bowfront tank and I put 2 MP40s on that tank. I know the ecotech website would recommend 2 mp10s for my setup and that would work initially, rather I bought for the long term and I have the 2 MP40s turned way down right now and that works fine. I also now as the flow needs increase the 2 MP40s on a 46 gal tank will be plenty as my flow needs increase.
