Thanks for your comments, Barry and sWORDs.

For the most part, the GC-100 response is near instantaneous. It's just occasionally the pause happens. Not generally when waking from the sleep state either.

As I understand it, the Pronto sends the asynchronous socket connect command then continues with any remaining code without checking for a connection - this is dealt with by onConnect. The delay therefore seems to be in making the connection or in sending the write command once connected.

I'm getting closer, but still not there!

Andy