Ingvar Stepanyan, author of the original 6to5 pull request has finished submitting a series of further optimizations via https://github.com/6to5/6to5/pull/736.
I'm clocking a 110-215X performance boost: 1,255,700 - 2,384,556 ops/sec! (on Chrome and Firefox alpha builds respectively) Check out the new JSPerf: http://jsperf.com/tco/17