Server/Client Performance Single host

I host a small 1.7.2 server for a few (<10) friends.

The javaw process running the server.exe utilizes significantly higher CPU when I launch my local client. Around 20-30% increase in server CPU usage vs a remote client logon from my laptop where the CPU load increase is typically 1-2%.

If I set the javaw server process Affinity to 4 of the cores, and redirect my client javaw to the other cores, basically forcing the client and server processes onto different CPU cores the server impact of my local client drops back into the 1-2% range of a normal client connection.