I figured out why `(+ 1 2)` is so slow in Nu. It was calling Arc's `or` which is pretty slow (compared to not calling it, anyways). So here's the new numbers, this time using the time library[1]:
As you can see, Nu is now faster than ar, but still slower than Arc 3.1. On the other hand, Nu's + is implemented in terms of case-lambda, so it should be better on memory in the case of only 2 arguments.