yea but your 7900 has 24 pipe lines. which inturn means your getting 13,200 fill rate persecond.. and he is getting 4,560 fill rate per second. but your overclock is average for a 6600gt.. and watch the heat! them cards get hott
As long as you arnt getting artifacts keep pushing it until you do, then back down a bit. Also make sure you have good cooling though, sometimes artifacts dont happen until about 5 loops through 3dmark 05.
i have a gigabyte 128mb 6600GT pci-e stock cooling
my best completly stable (16hours of 3dmark05) is 579/1303 if i go 1 mhz higher i get artifacts
btw i use riva tuner. i have tried coolbits, normal drivers and nubitor. this is off memory but i think i managed to get 4.2k in 3dmark 05 with system oc'd as in specs