In the 6 foot evap tower I built a couple years ago I used a danner supreme mag drive 5 (500gph). The flow at 6ft came out smoothly and kept my proc 0-1c over case temp. With the impellar mod the pump ran silent. It got pretty warm but never hot enough to the point where I couldn't hold it in my hand. The stronger models are fairly inexpensive and have good flow rate at high lifts. Here's a link to a
lift graph for various models.