Yes, you will see a difference.
With an ordinary D-sub connection, the signal is converted from digital to analog at the video card & transmitted in analog format to the monitor.
AFAIK, LCD's that use a D-sub connector as opposed to DVI convert the analog signal back to digital before it's displayed. So it goes from digital -> analog -> digital. With a DVI connector you eliminate all conversions, the signal stays digital until it is displayed.
Viper GTS