That is a synthetic benchmark. Look at and CPU Charts here on Tom's Hardware then select the E6400 (the E6300 will only be slightly less performance) and the Pentium D 830, you'll see how much better the E6300 is.
What version of sandra was it?!
I remmember Sandra 2006 CPU ratings were a bit absurde; A 3.0G HT P4 was rated 3958 while an Athlon 3000+ only 2985. Most of the times it couldn's read the fan speed etc.
Previous versions have had a lot of these problems but Sandra 2007 is pretty good at evaluating correctly almost everything.