Seti GTX 680 how many instance and help

I have a new gtx 680 and would like to know how many instance should I run on it?
And how to?

Does cpu make a big difference? Can I use my am2 250 x2 for this?

How much memory on the card do you have? I found that you can run about 4 instances per gigabyte.

you could use monitoring software to see the load % on the GPU.
running one instance on my 670 i was at around 80-85%.
two got me at around 95-98%.

i used EVGA OC Scanner X. dunno any others ATM.