I'm not an "expert", but I do fly mostly lower headspeeds, and have two E5's (stretched to 600 and 700), and a 516. on the 516 i'm using a hacker 1100kv motor, (A40-10L 8-pole) and the 16 tooth pinion. on 6s/5000 (I use venom packs in this heli, their 6s/5000 are equivalent weight to the 4000~4500's most people use). It maxes out about 2150 and I have it setup for 2100 and 1700 flight modes. +16/-16 on the pitch was original setup but i'm sure I've tweaked that so dunno the final number. motor is light, batteries light, so I have the carbon tailboom on it to get CG correct. With the lower rpms and high pitch, the tail is usually an issue on most machines and i like it very solid so I've sped up the tail with a pulley from stock drive products. synergy offers a speedup tail to 5.0 ratio, but I'm at 6.0 ratio. the way i fly, that holds at 1700, even with full stick sideways loops, but just barely. the normal 5.0 plus longer tailblades may also work but I haven't tried that. i generally get 10 minutes at 1700 and 7 minutes at 2100. Matt flew it and got a few seconds over 7 minutes at 2100 also. That is flying till telemetry says 4000mah is used from the 5000mah pack. Caleb Turner flew it at the Birmingham event and was really digging the 1700 setup so he flew at that rpm the entire pack, much smoother and more controlled than I, and went 12 minutes. i wish I had a slightly lower kv motor, like 1000, but don't. could probably get another 3 or 4% of efficiency in the total setup.