the multi is not locked at below 9x
the 680i chipset allows you to run linked or unlinked on the memory.which is very usefull.
so unless you are able to run insane front side bus, by lowering the mulit to 8 and cranking up the fsb, or just going for it at 9x youll be fine.
Nvidia has got a overclocking guide on their website, see if you can find it , if not pm me and ill email it to you.I have been overclocking for a while and it helped me with some of the oscure bios setting of the 680i
NEW RIG AND LOVIN IT
Q6600@3.45ghz w/ultra extreme,on a xfx 680I sli, ocz pc6400,sli'd xfx 8800 gtx, 2 seagate 500 giggers in raid 0,2 samsung 18x sata lightscribe burners, x-fi platinum,pc power and cooling 750 silencer, all wrapped up in a thermaltake armor