As far as I know, assigning an odd number of threads to a process should not affect stability.
As for performance I assume it would depend on the architecture as some processor architectures are designed to share cache between two cores.
Although when I tried to measure performance on a couple of tests with VMs, the performance increase was nearly linear. 3 threads being faster than 2, and 5 threads being faster than 4.
I guess my question is, are there any downsides that the community knows about when it comes to plotting with odd number of threads?
For instance on a 12thread system, plotting staggered with 5+5+1+1 (two phase1).