If the head conditions are a concern, then getting the 815 pump is recommended. If this situation only has a total of 5' elevation change, then the 809HS pump should be OK.
815 is the way to go in your situation. At 5' elevation change, you're at the end of the performance curve, so you'll just get a trickle at a time with 809.
I would also suggest a case for the pump, similar to the pump toolbox project in BYO. You'll be carrying that thing all over the place, so a protective cover and convenient on/off switch will be a blessing!