I go 27/6/13: http://www.swtor-spy.com/skill-tree-calculator/sith-assassin/11/?build=022132101121022002120200000000000312000000000000000000000000000003222100012000000000000000000000&ver=20
Do yourself a favor and go straight stalker/dps gear. You'll be able to tank and dps with that gear quite well. Get the survival gear after you've completed your dps set.