I may be late on this topic as the OP has already made an initial choice of headspeed to run.
Its fine to talk about headspeed, pack capacity and flight times for a particular flight style.
But theres another major factor that people haven't mentioned and it is GEARING.
So you could be running headspeed of 2300 using any of 12, 13, 14 or 15 tooth pinion with the 119 tooth main.
And depending on motor/esc choice some gearing combinations will work better and be more efficient than others at a selected headspeed.
I'll let others who know a whole lot more on the subject to decide if they want to comment on that as well...
For what its worth, I recently built my E5:
6S, Scorpion HKIII 4025-1100, Edge 120HV using 4400mah 35C Nanotech batteries while I'm getting used to the heli. Main gear ratio is 12/119
I now have about 20 flights on my E5 and am in a very similar space to the OP for flight style. i.e. circuits, 8s, loops, flips rolls, and some inverted flight.
Along the way I've tried governed headspeeds of 2000 up to 2300.
I'm finding 2200-2300 works nicely for the type of flying I'm doing and am getting 5:30 flights with about 30% left in the packs. I think I could stretch flight time to 6:00 at 2250 and land with 20% in the batteries.
Alternatively dropping the headspeed to 2150 I think 6:30 would be achievable, but right now I'm enjoying the responsiveness of the heli at 2250 rpm.
I'll try higher headspeeds as I get more time in the air and may try 13/119 gearing to see what difference it makes to flight characteristics and flight times at the higher headspeeds.
Just some food for thought.