Which server to be master and which one slave database?
In general (until very recent versions), it is better to make the Slave the beefier machine.

Originally, you could easily run queries in parallel on the Master, but they would be run purely sequentially on the Slave.  If the system is busy enough, the Slave could get behind.  Later versions have changed to RBR and added some parallelism on the Slave.

Also, if the Slave is getting 9 times as many queries (assuming of similar length), then it would be good to have a beefier Slave for that reason.