I went with the 3/4" ID tubing for three reasons
1) The ID of the stock FX5 Valve is 3/4"
2) the 1" stock tubing is ribbed on the inside (reducing flow)
3) I'm a cheap bastard and didn't want to spend $40 on tubing when I have 30' of the 3/4" in my basement.
Overall though, I really dont think I'm reducing the flow much if any? I didn't glue the spraybar either. Right now I have it pointed up and toward the back glass because the flow is still to much for the fronts. If I point it forward I get the "barrel roll" flow pattern and the fronts face forward to swim into the current. I think I'm going to enlarge my holes to 1/4. There a few sizes smaller then that right now, 9/32 or 17/64 cant remember which.
T5HO? I could have used it for my planted tank, if you asked me last year. =p