You can try increasing the PCIe x16_3, MHz to 106 - 110 range for stability at higher overclocks.
I always ran my 680i and 780i with the FSB - Memory Clock Mode as Unlinked and then I set both the fsb and memory speeds to whatever I wanted
As you start getting higher you'll need to increase the CPU Core, which we all do, but you'll also need to increase the CPU FSB voltage also. But the CPU FSB voltage is going to increase the temperature of the Northbridge, which is why I used a higher speed fan in the pic I posted. You said you already had a fan mounted, but you should get a fan with a higher cfm rating. I can't remember if it's a 60 or 70mm fan thou. You'll need to measure the heatsink, see picture and then order the appropriate fan (hopefully the 70mm will work)
60mm - Newegg.com - IPCQUEEN IPC-606010 60mm Case Fan - Case Fans
70mm - Newegg.com - Rexus TopMotor DF127015PH 70mm Case Fan - Case Fans
I always ran my 680i and 780i with the FSB - Memory Clock Mode as Unlinked and then I set both the fsb and memory speeds to whatever I wanted
As you start getting higher you'll need to increase the CPU Core, which we all do, but you'll also need to increase the CPU FSB voltage also. But the CPU FSB voltage is going to increase the temperature of the Northbridge, which is why I used a higher speed fan in the pic I posted. You said you already had a fan mounted, but you should get a fan with a higher cfm rating. I can't remember if it's a 60 or 70mm fan thou. You'll need to measure the heatsink, see picture and then order the appropriate fan (hopefully the 70mm will work)
60mm - Newegg.com - IPCQUEEN IPC-606010 60mm Case Fan - Case Fans
70mm - Newegg.com - Rexus TopMotor DF127015PH 70mm Case Fan - Case Fans