Memory, Performance, Throughput

For memory and CPU

top
iostat
vmstat
There's also an iotop, but I'm sure you'll find that PG is using most of the IO on a loaded db server.

For data throughput

You'll need a baseline for context.
iperf linux to linux)
ttcp (windows to linux)
whichever tool works between the source and destination. We don't need a super precise number to figure out what's going on. The difference between 80mb/s and 82mb/s isn't going to kill you, but if it's 80mb/s vs 8mb/s then you've got a problem.