Is it ok to use 4 application server against one database server?

Initially I have two database server (Master Master Replication config with Haproxy load balancing) A and B. And two application server say P and Q. Both P and Q is pointed towards A will move to B in case of failure. OLTP operations are huge in numbers per minute. Now we are adding two more app servers R and S. Just want to know experts opinion. Is it ok to point both R and S towards A? Or should I use B this time. Please suggest.