By SH I'm assuming you mean single hand. Neither of the Rio Iflight or Iflight short series of lines will pair with a single hand rod at all. The Iflight will be for 13' rods and Iflight shorts for 11'-12' rods.
Now if you are using a switch rod or spey rod... the Iflight series of lines are perfect for swinging in very fast or deep water where you're trying to slow your presentation down. Waaaaay down.
How do these outperform a standard Skagit head w/ a 5/5 MOW tip? Well... when you've dialed them in, the Iflights will allow one to get to the proper water level at a more level plane and not have the hinge effect... again in deep or fast water. Why does an angler care about hinge effect? It lessens ones feel for the fly and makes the perfectly presented broadside swung fly more difficult to achieve.
What I've noticed with swung flies... is that depth control and speed control of the swing are paramount to an anglers success. Too deep and you're hanging up in a run, too shallow and you're swinging well over the top of holding fish. Inches can mean the difference between a slow day and a hot day.
Can you still catch fish without an intermediate Skagit line? Yeah... it just takes a little fine tuning of your tip and fly to achieve the same result.
I've bought into the spey revolution and all of the various lines it has brought. There's almost too many out there now if you ask me. I carry a damn attache case with me full of various Skagit/Iflight heads and T-tips and MOW tips in various grains/sink rates to dial in my swing. I move around alot so I'm constantly changing things around. There's something to be said too on modifying ones swing with various mending techniques (upstream/downstream or multiple mends) and fly selection also.
That's my thoughts.....
ft09