I've always found stingwing conversions to work best as "stingwing fire warriors"
The speed can be attributed to a suit-type jetpack with no added armor beyond regular combat armor (using seeker missile rears and some bits), the gun can be a variant mix of a carbine and a blaster (powered up by the jet-pack's power source)
The Ld difference (and the WS, and in the past, initiative), explained by drugs that improve reaction times (to better control the engine with the limited controls of the superlight suit) but tend to cause nerve issues on most users, except a fw that get even more calm (strain leaders)
As for drones, I think grag covered most things.
Hardware is easy to explain, just model them with different hardware. not like we lack odd drones between interceptors, heavies, recons, remoras, turrets, etc. it can cover any difference in abilities such as deepstriking, the gun, the speed, etc.
The difference in drone mentality will be hard to explain in an army that isn't pure-drones (there its easy, "simple" drones are programmed to prioritize the safety of advance drones), why don't they protect others any more? why don't drone controllers work? (they work on remoras and turrets even, who are far bigger scaled)
In short, the reason they don't interact like other drones will be the hard thing to explain.