What do you mean by stable? Typically people will set CPU affinity when they are optimizing for applications that very heavily depend on L1/L2 cache or to reduce interrupts. You will probably find similar questions on stackexchange [1] or serverfault [2] and most appropriate would be [3] superuser.com. Best to ask on SuperUser to avoid being marked down.
Stability is usually related to kernel or application bugs. CPU affinity and priority will only help applications in that regard if the bug can induce high CPU load. Affinity will not mitigate kernel bugs.
It is probably best to let your kernel handle process scheduling unless you have a specific need otherwise.
[1] - https://unix.stackexchange.com/
[2] - https://serverfault.com/
[3] - https://superuser.com/