>'Safe' programming languages will improve security, presumably at the cost of usability through decreased performance. A bit like how a Ferrari is faster than a Volvo, but not as safe.

This is fundamentally untrue. Safeness of the kind described in the article does not come at the cost of performance -- all type checks, invariant conditions and general formal proofs of correctness are determined at compile time. The produced code is to be indistinguishable from a correctly written, efficient C program. You are allowed to play as much as you like with direct memory accesses and use all the dirty tricks you like as longs as you can prove that the resulting program is formally correct.

What could be argued is that price you pay for all this is the difficulty of writing such programs. But definitely not their performance.