I would say if a startup overhead time of < 10 second bothers you, you're not working with "data". Of course sed and grep have less overhead, but I wouldn't even thin of trying out a new tool for files/datasets larger than, say a Gigabyte. (Rough guess, I know you can use grep and sed in under 10 seconds for larger files, the point is about perspective and complexity.)

Clojure is sadly a really bad choice for fire-and-forget cli scripts, but "large scale data processing" doesn't fit this criterion for me.