8 vCPUs, but how many cores? 8 sounds like a small number for that environment.
How many concurrent users are there typically? If typically only query runs at a time, set it to 0, so that query can get all cores.
But if there can be multiple users, having a query that takes all cores is not that great. But if you only have eight cores, what can a poor boy do? If you set it to 6, there is some space for small queries, but all parallel will fight about the CPU.