8800 GTX O/C Problem!

Ok, so i have a eVga 8800GTX and i have had it oced to 620/1500/1000 ever since i bought it. Every time i tried to o/c it further with the stock cooler it would start to artifact. So i decided to get an hr-05 plus and i slapped it on my card with a 120mm yate loon (50cfm) and some as5. My idle temperatures went down about 15c and my load about 20c. So i tried to o/c the card even more lowering everything to stock (576/1350/900) and gradually increased the core by 10mhz, i got it up to 660 with my idle being around 50c and loads never over 65c though it would crash about 5 min into 3dmarx 06 and would continue to do so until 630mhz where it would just artifact. So even after the after market cooler i can only run the card 100% stable at 620mhz which is really urking me . I was wondering if anyone had any input or could point out something that would help me in getting the core higher than 620mhz so i don't feel like i have wasted ~$60 on nothing more then some cooler temps... Thanks

Btw when i took my stock cooler off i saw a -3 (looked like it was done with a sharpie) marked on the copper base where all of the thermal paste was, does anyone know what this is?

Well the card itself was bought 32 days ago from newegg, but i checked the bios version and it is 60.80.0a.00.01 meaning that it is rev 7 out of the 8 their are.

yea i tried it at 900 and it made no difference, i think the chips with the sharpie writing is Evga's way of saying the chip is just crap.

I get 680mhz/1000mhz on my 8800GTS
Runs every game stably, but I heard Crysis is demanding, causing artifact on a supposedly stable overclock.

Anyways here's why you can't overclock your core further:
When increasing the core clock, the shader clock increases also. Usually the shader clock is causing the artifact. Finding this problem, I used Rivatuner and clicked on some settings to enable shader clock. Then I selected "unlink frequencies" so they both don't go up when overclocking. Before I could only get 633mhz before artifacts starts appearing. Now I get it stable at 680mhz after unlinking the frequencies. My true speeds are 680mhz/1620mhz/1000mhz.

Here's the link:
http://www.guru3d.com/newsitem.php?id=5958

EDIT: Once the settings are enabled, the test function disappears. I should warn you not to get all crazy in the clock speeds.
Good luck

Wow, for some reason that never crossed my mind. I should try and unlock my shaders because I believe my core can go mutch higher than 700,8800GT, I have read sigs around 740/1080. The highest no artifacting I got was 710/1040 Thanks for that piece of info.