Question abount memory

So I currently have 8 gigs (4 x 2 gbs) pc2-8500 g.skill memory. Currently these modules read 800 mHz at 5-5-5-15 and the voltage is auto. My current mobo is Asus striker II formula with a FSB of 1333 mhz. I currently have a q9300 cpu quad 2.5 ghz. I was wondering now these modules are supposed to run at 1066 mHz, but they run at 800 mhz. I know I need to change the voltage and unlink my fsb and memory but from what I hear 8 gigs pc2-8500 doesn't always run stable 1066, so I have a few questions:

1) Is it better to run 4 gigs at 1066 then 8 gigs at 800 mhz?

2) Anyone know if 8 gigs would be stable at 1066?

3) How would one test if they are stable?

thank you sir.