The 550 Ti should be faster than HD 6770.
The 550 Ti requires one 6 pin power connector.
6-pin power connector looks like this- http://kablammo.strongerthandeath.com/wp-content/uploads/2009/04/six-pin.JPG
You don't have to worry about HDCP support it has been available long long time ago.
3d support and HDCP is different.
If you want support for Phsyx and CUDA you should go with Nvidia.