For serial connectivity, I always just use a terminal server (like from Perle). They're just boxes that allow you to make serial console connections via ssh/tel

For serial connectivity, I always just use a terminal server (like from Perle). They're just boxes that allow you to make serial console connections via ssh/telnet over a TCP port (or if you must through a virtual COM port driver). These are used widely in datacenters to connect to switches which have serial console ports for configuration. They're not unreasonable in cost (start at like $100 for 2 ports), tons of features, and not flaky like the USB-rs232 adapters. Not so sure about latency, but throughput is fine.