What is faster? KVM or VirtualBox? Windows 7 definitely faster in VirtualBox. What about Whonix?
What about graphics? VirtualBox used to be a lot more snappy wrt to multimedia playback. Is this still the case or has changed?
More in-depth graphics comaparisons are expected between the two this year.
However some benchmarks  in that article already show superior results for KVM.
 H.264 Video Encoding, Phong Rendering With Soft-Shadow Mapping
Vbox’s new 3D GPU has very lackluster results and only covers extensions up to OpenGL 2.1
I would expect that KVM is faster because it has direct access to hardware and thus one fewer hop for syscalls, but I don’t see any mention of speed in the ‘Why Use KVM Over Virualbox?’ section of the wiki.
A thread in the forums titled ‘Who is faster for Whonix? KVM vs VirtualBox’ seems to convey that KVM is faster, but this thread is from early 2019 and so possibly outdated.