LatencyMon

LatencyMon is a good tool for testing the overall system responsiveness. The app checks whether your device is suitable for handling real-time data streams. The "highest measured interrupt to process latency" reading shows a worst case scenario of how quickly your machine can shuffle data between its hardware components and the software that needs to process it.

Since I noticed the high latency of Prime95 Large FFT I ran the test three more times. The results remain around the same values. Still, it's worth mentioning that I didn't observe any real-time system slowdowns while the benchmark was running.