I inherited a like new base model 13" mid-2011 i5/128/4. It's still running Lion with approximately 65 battery cycles. Windows user bought it, tried it for a while, and put it back in the box. It's snappy on Lion but I'm wondering if I should update the OS to gain more features. For those who have updated, which OS would run the best without losing functionality? Version 10.8: Mountain Lion Version 10.9: Mavericks Version 10.10: Yosemite Version 10.11: El Capitan Thanks in advance.