Are the new serves physical or virtual? I know you only wanted app, but the most important thing for DB server RAM is to configure HugePages/Large Pages.
On app server, edit your $CONTEXT_FILE
increase s_oacore_nprocs to 4
Increase s_jvm_options to -verbose:gc -Xmx2048M -Xms2048M
The biggest memory consumer in r11 apps is 64-bit planning, but you can only get that on Solaris, HPUX and AIX.
What are the OS versions, and current and expected RAM values on the servers ? How was the conclusion that more RAM will result in better performance arrived at ?