When I plumbed our new equipment I never even though about low head amount. Our Northstar pump allows for a 2" connection from pump to valve, so I used 2" pipe, even with a 90 degree elbow in it. its such a short run from pump to valve I didnt think much of it.

As far as flexible PVC........Ive really only seen it used underground (although our original equipment had it above ground too). The problem with it above ground is......weedwackers! I had our lines pressure tested before determinig if we should save the pool, and there were a couple gashes in the flexible PVC where they left the ground. ive since converted everything above ground to rigid PVC. Granted you can cut that up pretty well too, but I just stay clear of the equipment with the trimmer (and this year Ill finally dig out around the equipment pad and put in gravel so I dont have to trim around it anymore).

Good luck.

-Chris