Yes, if speed is your key issue, I think USB is the way to go.

Note that the delays in TCP/IP are inherently variable & unpredictable - could be an issue in this application?
USB has various modes, including ones with guaranteed delays, guaranteed bandwidth, etc (it's designed to cope with audio, after all!) - could be applicable here?

For a simple bolt-on USB interface to any parallel port, take a look at the FTDI USB modules.
They do free drivers for easy PC connectivity.

The 'Search' on this forum will find several references - and here's one I prepared earlier:
http://www.antronics.co.uk/USBMOD2/ - with links to their website and some useful magazine articles.