pump suggestion

[lastlight]

So here's the dealio:

Picked up a new chiller thanks to a super-generous Abchaos and now I need to bring it online. The chiller will be in the basement as close to the ceiling as possible to reduce head pressure and the pump will run externally next to it. I will need to get a siphon going to prime the pump but only once. The chiller requires about 500 gph (Pacific Coast CL-650) and I've been told the unit will add roughly 4 feet of head. Water will siphon from the sump to the pump next to the chiler then be pushed back to the sump. The vertical distance between sump and pump will be another 4 feet roughly.

I'm unsure if the 4 foot drop counts in head loss because in a way it's like putting a chiller inline in a closed loop. From what I understand a closed loop has no head loss and the pump could in theory be 4 feet below a tank or 50 feet.

I'm choosing an external install for two reasons: don't want to pay for a pump that's powerful enough AND quiet enough for the livingroom sump and space is tight in there as it is. I'd love to use another eheim internally but at 900 gph at zero head I doubt a 1262 would be up to this.

So before I spend a few dollars any suggestions?

I was thinking a mag 12 or quiet one 6000. I then have the luxury of valving each back a little if need be.