Yes, I believe performance of same Qemu version on Linux or Haiku would be fairly close. Only benching would show if true or not.
Drive install is not always an option. I have x86 Android OS. Tried to boot and would not even with the VESA driver. Also, others download OSes (like Haiku) and it will not boot for them or crashes. Others download OSes they try out couple of times and then delete them. I have downloaded Haiku images and sometimes not worth installing to thumb drive if I will install newer version in couple of days. Sometimes I just want to check something out real quick in Haiku but prefer not rebooting, ie, I give help on forums and being able to check in Haiku helps which can quickly be done through VirtualBox without rebooting, etc.
Also, with hardware V, Haiku (and other OSes) run pretty good in virtual machines.
Also, you could do what you say with just 1 thumb drive with good size like 8GB. Partition it, install OSes, install boot manager (like Grub) and create a multi-OS thumb drive. =)