Doubt you need v-synch on with a 5670. Have you tested to see if you get any tearing without it?
I only mention it as mainly v-synch is designed to limit your FPS to the frequency of your monitor (usually 60hz) so you will never get over 60FPS with v-sync on.
It would help to know which CPU you are running and which OS and also your monitors max display resolution then the advise that can be given will be right for your system