I had a python server written in Python with greenlets to hat I switched to PyPy and the load it could handle went up maybe 4x. (5k per second to 20k per second. I took two weeks to switch to go and it went up another 10x to 100k per second and had less bugs (in fact a parsing bug in the python caused messages greater than 64k to be dropped; the Go handled partial reads properly and starting sending 2M msgs (to Kafka). The subscribers started getting the long messages and barfing making the system go wonky. Oddly all the giant messages were corrupt data anyways.

Code size was about the same due to stuff being implemented in Python manually being handled by Go runtime.