Thanks for the information. Although retired now, I've been involved with micrometeorology throughout my working life. This quadcopter lark is just one of my retirement hobbies, and it is all new to me. So this is all just a "proof-of-concept" project and I have been trying to keep costs down to a minimum until I'm aware of limitations in both my choice of drone items and what I can feasibly do. This not only applies to FC's but motors, frames etc. My first scientific project is to get a fast-response fine-wire thermocouple to ascend through the boundary layer (0-100m) and use the statistical properties of the data to give me a profile of Sensible Heat flux. Similarly, this method can be used to provide data at a fixed height over a ground area to gain a picture of the variation in Sensible Heat flux over different terrains. So this will all be line-of-sight operation but with control via the GPS and altimeter. A colleague is developing a lightweight (200g) photospectrometer - so that we can then do vegetation surveys. Eventually using lightweight sonic anemometers that the Arduino community have developed, I can move into full energy balance studies of the boundary layer.
I'm not planning telemetry if you mean FPV - and my data collection will be to OpenLog Datalogger SDcards - not back to ground station.
But I will have a look at the FCs you mentioned and bear your suggestions in mind - and thanks again for your input.