External Pump Question 3800 - 5000 gal

A good vendor or manufacturer will ask for the exact specs of your setup and do the math to determine your total dynamic head in order to recommend the appropriate sized pump. Note that just because you are pumping water 10' vertically does not mean you only have 10' of head pressure; horizontal runs, elbows, valves, running water through a filter etc are all going to add to your total head and should be considered when sizing a pump to your system.

The lower you keep your total dynamic head (by either reducing the height of your gravity filter or using larger plumbing to reduce friction loss within the pipe) the smaller the pump you can use to achieve your desired flow. Designing a system with low energy requirments can save you tons of cash over the years, so since you are in the planning stages, I would take the time to make the system as efficient as possible.

I have heard good things about the following pumps, although I have no personal experience with them:

W. Lim
Sequence
Artesian Performance Pro

PS- You may want to search the forums on Koiphen if you are looking for first hand exeprience with these pumps...lots of good info there and it's more geared toward ponds.