Hey guys, ive had this MSI 8800gts 512 OC edition for a while now, and im wondering why GPU-z shows a different clock speed than what the manufacturer promised me?

The manufacturer states, as well as 3 other review pages:
730 mhz Core
1940 mhz memory
1825 mhz shader

While GPU-z shows:
678 mhz core
1944 mhz memory
1728 mhz shader
is it showing it accurately, or do i have a faulty graphic card?
Any good programs to overclock with?