Microsoft posted this benchmark test on performance differences between using SQL 2000 vs 2005 and SharePoint Portal Server 2003.

One thing I would note is that they are using 64bit platform for the SQL Server. Due to the performance enhancements in 2005 to take advantage of the 64bit capabilites, I can see how quite a lot of the performance difference is more efficient use of the hardware. Compelling reason to upgrade if you can !

I had installed this way and did some limited testing. i thought it was faster but I had not taken time to do any scientific testing :-)

Steve