A single pickup system can supply a lot of oil, so if your combo is well thought out I don't see any reason to run an extra pickup line. Another thing to think about is you have two lines between the pan and pump but you still only have the same area of opening in the swinging pickup. So just how much help can the extra line add?
My bet is the only time a dual pickup system helps is when the demand is very high,(too much clearance) or the oil is too cold.
When I was running the no growth radials, my motor was going through the traps at 7800 rpm. No problems. I now go through at 7400 rpm. Thats all I have, is a single line.