Let me know if the following description of your requirement is correct - or if I am wrong please correct it
30 times per second ...
Your PC program sends 6 messages of (how many?) bytes each to the master Arduino
The master must interpret each message from the PC to figure out which slave should receive the data
The master sends 9 bytes to each slave
The slave sends (how many?) bytes of data to the master
Just doing some rough calculations if the master was to send separate messages to 6 slaves 30 times per second that would mean sending a message about once every 5 millisecs. That is very close to the capacity of the system.
The network and mesh libraries build on the basic RF24 library and add considerable overhead that will hugely reduce the throughput.
You have not told us what data the slaves need to send to the master.
More importantly you have not explained the project you are trying to implement so I cannot see why the performance is needed or whether some simple alternative might solve the problem.
...R