I disagree, I think the 70% is right, and matches what you still describe as a 1.7x speed increase. If it originally took 4 seconds and now takes 2, I'd call t

I disagree, I think the 70% is right, and matches what you still describe as a 1.7x speed increase. If it originally took 4 seconds and now takes 2, I'd call that a 100% speed increase, i.e. twice as fast.