Folding@home on CPUs is ineffective, compared with GPUs.
On the other hand, there are many Distributed Computing projects out there which cannot run on GPUs and need every CPU which donors can spare. (IOW, CPUs are going to waste at Folding@home.)
If you are particularly interested in medical projects, these ones are currently (and pretty much always) active:
As to your original question, if the computer will be dedicated to Distributed Computing, get the cheapest which is immediately available to you, with as few features as possible. I for example preferred mainbords with Gigabit LAN over ones with 10G LAN, since Gigabit NICs consume a little bit less power, and PCIe v3 over PCIe v4 again for lower power.