[hinkley]

You've dodged the question mark. What does 50% faster mean? What does 67% faster mean? What does 75% faster mean?

I'm using the exact same terminology, so splitting hairs on phrasing isn't going to work for me.

[mattkrause]

Something crawls along at 1 m/s.

After some clever engineering, it now runs 50% faster. Its speed is now 100% (baseline) + 50% (improvement) = 150% of 1 m/s (original speed) = 1.5 * 1 m/s = 1.5 m/s

The budget option runs 20% slower than the original model. Its speed is 100% (baseline) - 20% (derating) = 80% * 1 m/s (original speed) = 0.8 m/s.

[aordano]

As sibling comments said, 50% faster means adding 50% of the nominal speed, so it's 1.5x the original magnitude.

[fragmede]

50% faster means original speed plus 50%, or 1.5x