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).