[xnorswap]

But 70% more stuff in the same time is 70% faster.

[OJFord]

Let's say you do 10 things in 100 time (100/10 =10 time per thing) to start with:

70% more stuff in the same time is 17 things in 100 time (100/17 =5.9 time per thing);

70% faster is 10 things in 30 time (30/10 =3 time per thing) - or, I would argue incorrectly, perhaps said to mean 10 things in 70 time (70/10 =7 time per thing).

[LanceH]

90mph is 50% faster than 60mph. 17/time is 70% faster than 10/time.

You're describing "in 70% less time", not "70% faster".