This might be pedantic, and I'm sorry, but this is something I always wonder about when I talk about performance.

When we say 1.7x faster, what is a fast? How does fastness increase? It's nearly 2 fasts instead of one?

I think the compression sample you gave is much better. Multiply the original file size by the factor to get the new, compressed file size. This is much better than a statistic that I hear a lot about the compression in a columnstore database we use, where everyone says "7-10x compression", because that was published first and is popular.

I'd prefer to see something like your compression example. It took 8 seconds before, and now takes 2. My optimization makes the operation take .25x the time.