When we talk about using abstract classes and interfaces in programming, it's important to know that they both have different roles. They might look similar at first, but how they work and when to use them can affect how fast your program runs.

Abstract Classes:

• They help you reuse code. You can create abstract methods (which are like placeholders) and concrete methods (which are fully developed). This means that other classes can use what you’ve already written, saving time and effort.
• Abstract classes can hold data with member variables. This makes some tasks easier, but if not handled well, it could slow things down.

Interfaces:

• Interfaces are mainly about setting rules for how things should behave. They do not provide any built-in methods. All methods in an interface are abstract, meaning they don’t have a body.
• With new features, interfaces can have some code called default methods. However, they are designed to be simple and don’t keep track of any state. This leads to cleaner designs.

Performance Points to Think About:

1. Memory Use: Abstract classes can use more memory because they store data. Interfaces, on the other hand, don’t keep any data, so they usually use less memory.

2. Method Calls: In programming languages like Java, calling methods from abstract classes might be a little quicker than calling those from interfaces. This is because of something called virtual method tables. But honestly, the speed difference is usually so small that it won’t matter for most programs.

3. Testing and Keeping Code Clean: Interfaces are great for separating different parts of your code. This makes it easier to maintain and improve your code, which can help with performance later on.

In short, deciding whether to use abstract classes or interfaces should depend on the needs of your program, not just how they perform. While abstract classes might have some small benefits at times, interfaces are better for keeping your code clean and organized, which is really important in today’s software development.