So these options only exist on the pooled RedisClientsManager and you can basically think about it like a database connection pool. Each item in the pool maintains a connection to Redis, the architecture of redis (i.e. event-loop) means that connections are really cheap, so you don't need to worry about hurting redis here, what you want is to aim for a number that is around your max concurrent connections or perhaps 2x your average concurrent connections so you in most cases your requests are not blocked waiting for a connection to be free.
At a guess at a tangible number I would guess somewhere in the range of 10-100?
Note: The if your redis server is on the same server then its best to use BasicRedisClientsManager which provides no connection pooling but is faster because establishing a new TCP connection on localhost everytime is effectively a NO OP so there are no inherent benefits of sharing a connection.
Hope this helps!
Cheers,