Purely based on specs (we'll have to wait for someone to do the tests to confirm), I'd say there should be little difference in runtime at similar output. Although the specifications on the fenix-store.com website say something different (they list the 18650 model as having a longer runtime)
They main difference between the two is that the TK11 can be used with rechargeables. And since the TK11 can also be used with primaries, I'd think that the TK11 would be a more versatile choice. But maybe there are some other differences, that can't be read from the specs, so I'm very curious about the first reviews