Currently flying an E5/600 on 6s/5500's. 605 mainblades, 105 tailblades, the 4.9 tail speedup, then some modified gears in the rear to bump it up more. Tail ratio is 5.45 to 1. Flying at 1500/1700/1900 for the three rpms. Started with 16 degrees pitch, but have tweaked since I built it last year, so probably a degree or so less at this point. It should be well under 9 lbs, I just forget what it was when weighed. My "super stretch" E5 with 700's and 12s/4350 is 9 and 3/4 lbs. Each 6S/4350 is 20 ounces, where he 6s/5500 is 28 ounces, so 28 versus 40 for battery weight gets the number to 9 lbs. I'm also using a motor that's physically smaller and lighter in the 600, and then there's the weight difference in boom,blades,esc. (edge hv80 plus BEC pro in the 700, talon 90 in the 600). I like 1500 and spend most of my time there (except when night flying, for some reason I like to rip around at high rpm at night). I really like using 5S/5000's~5500's, which I do quite often. My motor/gear tops out at 1600 plus a few rpms on 5S, but it's of course lighter, and I can spend the entire flight in the 1500 mode without getting the talon 90 hot. At the low weight, at 1500, it's great for smooth, "geriatric 3D". Flying a mix of the rpms, switching around during flight, I normally go 8, sometimes 9 minutes, on 6S,.. and 10 to 11 minutes on 5S at 1500 the entire time.
Stock head dampers, and shimmed pretty tight too, with no wobble.
As for your original question,.. 1500 seams pretty low compared to what is "common", but it feels fine flying, plenty of performance assuming sufficient pitch. 1400 works but gets a bit too soft on collective for what I like with the 600.
