For that setup 1000W is over kill. You could run two 980 Ti's on a 1000W PSU. Save some money and go for a 750W PSU, leaves plenty of head room for upgrading in the future as well. In my personal opinion you should only purchase brand new PSU's rather than used or refurbished ones, since it's basically the thing that can make or break your system.
Just my two cents :)