> Typing generally slows down languages, not speed them up because of all the additional checks that must be done.

Source? You seem to be talking about compile-time versus runtime, and I've not even heard of compile times being significantly slowed by type checking.

> The dynamic stuff is part of what slows down languages like Python and makes them tricky to optimize.

That seems to harm rather than help your previous claim. In untyped languages, in principle every object has to be treated as dynamic.