return pump question possibly a panworld

[cdh9400t]

Im looking at getting a panworld pump for my 125 gal. reef, im just not sure which one to go with. I have a dual hangon rated at 1200gph, so my goal is to get 1000gph return. its a toss up between the 50px-x and the 100px-x. would either one of these give me the right flow without out flowing my skimmer box, or would I be able to use 2 1inch tubes as my siphon tubes instead of the 3/4inch ones to give more flow. O and my return is about 5ft up. nothing drastic,

[davocean]

Actually I'd rec more like 600gph for a return, so like an Eheim 1260 or an oceanrunner 2500.
That gives close to 5x turnover