Openfire with Java x64 or x86

I have 800 people right now will be going upto 1500 people soon. There is a mix between web spark and full spark.

Server is a VM so ram and CPU can be increased on the fly if needed.

Is it better to use x64 Java or the normal x86 Java on Server 2008 R2 64Bit.

Also I tried in the past to get the x64 working but I can never figure out how to get spark to properly detect it does anyone have a step by step for setting up Java x64.