One thing to keep in mind is that with both the /PAE and /3GB switches, the server will only be able to access up to 16GB of RAM on the server. This will only be a problem if you have more than 16GB of RAM. If you do have more than 16GB of RAM on your database server, then you may want to consider either /PAE or /3GB, but not both.
The OS account that starts the instance must be granted the 'Lock Pages in Memory' system privilege. Also, when setting /PAE, your cache must be sized with the DB_BLOCK_BUFFERS parameter. And it is a good idea to set USE_INDIRECT_DATA_BUFFERS = TRUE in your INIT.ORA config file.