Performance etc

I’m new to FreePBX, but I’ve got a instance up and running and it seems like a great product.

How does it perform? In the sense of how many users/extensions is it capable of handling on certain hardware etc.?

I’ve read a lot about Kamailio (, the former OpenSer. How does this compare to FreePBX and are there any sense in putting a Kamailio instance in front of FreePBX (on the same server?).

If anyone can help me out, give me some pointers etc. it would be very great.