So, these are some (very unscientific) screenshots of CPU usage during system idle, Reaper Playback and Reaper recording. During reaper recording the CPU never went above 1.51GHz. So there is still a bit of headroom. Most of the time the CPU was hovering around the 1.20GHz. I was recording on one track with one microphone.
Idle
System - Idle CPU usage.png (Size: 91.06 KB / Downloads: 470)
Playback
Reaper - Playback CPU usage.png (Size: 103.34 KB / Downloads: 442)
Recording
Reaper - Recording CPU usage.png (Size: 96.66 KB / Downloads: 455)
Idle
System - Idle CPU usage.png (Size: 91.06 KB / Downloads: 470)
Playback
Reaper - Playback CPU usage.png (Size: 103.34 KB / Downloads: 442)
Recording
Reaper - Recording CPU usage.png (Size: 96.66 KB / Downloads: 455)