HIS HD3850 IceQ3 Turbo (AGP) Questions

Hello,

I have Radeon HD3850 IceQ3 Turbo (AGP) and a few questions as well:
1) The card comes with 1 x 8 pin power connector, but my PSU (HEC 500W 2.0) has 2 x 6 pin ones. At default speeds (720/1820) card runs OK, but when it gets overclocked (840/2008), becomes unstable and its GPU gets reseted by driver. I'm asking because that before crashing card works as if it was not overclocked: there're no artifacts at all, even with most demandant games. I guess it is in lack of power due to 6 pin connector. So buying 6 pin to 8 pin connector would solve my problem?
2) All 3DMark's run fine, except 05 (tried all versions available, applied a hotfix). The loading screen gets always blurry and the all tests provide very poor graphics. Result is lower than 3DM06! What is this caused by? Driver?

My PC:
ASUS P4C800 MB;
P4 EE @3,66GHz CPU (Northwood);
2,048MB of Kingston HyperX Ram (500MHz, CL2);
2,5TB HDD (4 drives);
HIS HD3850 IceQ3 Turbo (AGP) Video Card (ID 9515) (With cat 8.5 AGP Hotfix);
HEC 500W PSU (2.0).

CPU and RAM are 100% stable.