Tsunami is supposed to make really good submersibles. Sounds like you need a pump to push 5000 gal at 11' or more of head. You will find if you install an external pump your electric bill will give you a noticeable reduction in operational cost. You mention pumps not pump. What circuits do you run them on? Do you have a pressurized filter?
Figure 5000 gph for the pond volume (one time per hour turn over), 10 feet of head for head height, you need to add up the length of your pipes and fittings, and include pipe diameter, then check the chart for friction loss. This will tell you what gph pump you will need at what head loss—height plus friction loss. Do you run all the pond water over the falls?
Most reputable pumps will have a chart that shows gph vs height of head.
http://www.aquaart.com/pondFLC.htmlYes stay away from Cal pumps...
External pumps: W. Lim or Artesian are good.