Ok, KVM is for hardware virtualization on Linux and maybe on BSD too with their port. So, when using KVM with Qemu then it should run fast like VirtualBox but currently Haiku does not support KVM and likely will not for R1.
Qemu on Windows 7 also does not support KVM and stuck with 0.11.1. Windows 7 is the OS I mostly run now.
Also, Qemu emulates the CPU type. That slows things down. Not sure if this happens with newer versions since I have not tried Qemu past 0.11.1. That is why Qemu is called an emulator. VirtualBox passes my actual CPU type to the guest OS - no CPU emulation.
Qemu is only fast on Linux using KVM otherwise it is slow for the rest of us because we are stuck with 0.11.1 version that uses kqemu acceleration!
KVM seems to be only on Linux (and maybe BSD). So, that is the only OS that can run Qemu fast.
VirtualBox is available on Windows, OS X, Linux and Solaris and should support hardware V on all of these OSes. Since I will run Windows 7, Haiku and maybe Linux, then it makes sense to stick with VB.
Also, when doing the 7zip test Qemu+kqemu took over 13 minutes. I stopped it because I could not take waiting for it to finish. Ran really, really slow!
Consider that any hardware virtualization on Haiku (like KVM) would not appear until R2. Since Qemu+kqemu is super slow and Virtualbox with software virtualization runs much faster than Qemu with software V then which is better for Haiku? =)
With hardware accel they maybe equal but only if Qemu stopped emulating the CPU. I cannot say without testing it out myself. But with software accel, VB beats Qemu hands down!!! No contest!!! Haiku would get software V for R1 & hardware V for R2 with any virtual machine software.
PS Michael Lotz, Haiku dev, worked on Qemu port and was able to get it to 0.11.1 but nothing newer than that because of KVM. With VirtualBox, should be able to port the latest version and just use software V mode until Haiku supports hardware V.