After experimenting with running Folding@home in both a VirtualBox Linux x64 machine and under Wine, I have come to the conclusion that most people would be better off running Folding@home SMP2 under Wine.
1) You can install the Wine PBI whether you have a 32 bit or 64 bit PC-BSD installation.
With VirutalBox, to run the 64 bit Linux installation, you need to have a 64 bit PC-BSD installation.
2) VirtualBox requires a certain amount of dedicated resources to run - 512M to 1024M of memory, a piece of your video display memory and hard disk space. Under Wine, the memory requirements are dynamic but are typically less. There is no demand on the video card. Hard disk space is limited to the program and the work file.
3) VirtualBox needs a dedicated kernel module to be loaded. You do not need this with Wine. This means less overhead on your system.
I have hit some issues with power management and the VirtualBox installations but if you keep power management settings simple, both should run well.
Instructions for setting up Folding@home under Wine and VirtualBox are here: