Something can be fast, but lack efficiency or the ability to utilize the speed.
For example, a car can have 1,000hp, but utilizes a large turbo which takes a long time to spool up, leading to poor performance. It may also have poor handling characteristics.
On the other hand, let's use a car like a Mazda Miata, which only has 181hp. It is not fast, but it is an incredibly performant car, with exceptional handling and driving dynamics.
Speed and performance are not directly correlated, and are independent metrics. Performance is more of an indication of the overall dynamics of action, intention and results.
What's the difference between fast and performant?