Let me elaborate. There are no tail calls. The GC is not suited to functional programs (lots of small, short-lived allocations) (though that has been improving recently). No first class functions (you have to make an object with a method instead). I might be wrong, but that's a significant overhead.
WUT? That's _exactly_ the thing the GC is good at, and it's that way not since yesterday.
The limiting factor is the speed of allocation (no GC involved), not GC.
That's how OCaml does it. I'm not sure how to do it concurrency-safe, though. Maybe using small per-thread heaps that get collected whenever an object is shared between threads, or by statically inferring which objects can be shared and which are thread-local.
That's also how the JVM does it. You can criticise the JVM on some things, but GC performance is not one of them. You should really make sure you're better informed before posting FUD like this.