If you read the forum threads on performance issues, what they generally come down to is type-hints & using Java types. The problem is that idiomatic clojure doesn't perform well (it may scale well but you throw away a bucket-load of performance by using it anyway). The way to get truly good performing Clojure is to write Java...

Pixie does look promising and is more my type of thing (coming from a low-level background) but I haven't managed to have time to look at it properly yet tho.