I am still breaking my engine in, but I get a full minute longer flight time than my friend's N5C with the OS55 HZ or whatever the designation is. I need to look at my timer next time out, as I am leaning it, but I get over 6 minutes for sure.
What are your needle settings and how many tanks (or gallons) do you have through the engine.
As for head speed- I am still working this one out. I typically like lower head speed on my machines, but I have been bumping it up to see where the happy spot is. I think I am around 2150 to 2200 right now. I need to confirm this though!