Earlier quoted context omitted.
Opus really is great. My first choice almost all the time. Except... I wanted to stream music across the network to another computer with the lowest possible latency. I didn't care about the extra quality you get from lossless (opus sounded fine to me at 96kbps), but chose flac because it has almost no latency. Opus (and for that matter, all other codecs) added noticeable latency.
Something's wrong with your setup. Typical latency for opus is only ~20ms and you can get it lower than that by changing an encoder setting. FLAC is usually more than that, but it should be negligible regardless. Maybe you are trying to decode Opus on an extremely low power device?
Overall I just found flac to be rock solid and lower latency without much tweak