I'm excited to unveil the first ever (to my knowledge) eGPU SLI configuration. 2x 780 Ti's + 2x Sonnet SEL's running on a 2013 MacBook Pro.
http://forum.techinferno.com/diy-e-gpu-projects/7326-sli-success-2x-780ti-2x-sonnet-sel-macbook-pro-%4032gbps-tb2-2x-16gbps.html#post100318
http://forum.techinferno.com/diy-e-gpu-projects/7326-sli-success-2x-780ti-2x-sonnet-sel-macbook-pro-%4032gbps-tb2-2x-16gbps.html#post100318