When developing a cross-platform GUI, consider the following performance factors:

1. Rendering and graphics processing

2. Event handling and response time

3. Memory usage and management

4. Startup time and initialization

5. Resource utilization (CPU, GPU, RAM)

6. Power consumption (mobile devices)

7. Network and communication overhead

8. Data storage and retrieval

9. Multithreading and concurrency

10. Platform-specific optimizations

To optimize performance:

1. Use native GUI components and APIs when possible.

2. Minimize platform-specific code and abstractions.

3. Optimize graphics rendering and use caching.

4. Use lazy loading and on-demand resource loading.

5. Implement efficient event handling and processing.

6. Monitor and optimize memory usage.

7. Use profiling and benchmarking tools.

8. Test on various devices and platforms.

9. Consider using hardware acceleration.

10. Continuously evaluate and improve performance.

By considering these factors and optimizing performance, you can create a fast, responsive, and efficient cross-platform GUI that provides a great user experience.