The Seasonic is modular and 80+ gold. If you won't SLI I would pick the Seasonic over the Antec. @Abkaflab the Seasonic has 2 6+2 pin pcie connectors. That will not work for sli/cf since most cards need 2 6 pins. You would need 4 6 pin connectors to sli/cf, which the Antec has.
Are there adapters you could get to make xfire an option?