Differences Between Server 8 and 9

I have Server 8 which I had to purchase when I really wanted Server 5.5 
(which I got as a free downgrade) to go with my FMP 6 seats.

Now I have to move up. My choices:

1. Buy FMP 9 seats and ask for a downgrade to FMP 8 seats so I'm running 
an all Version 8 system.
2. Run Server 8 with 9 clients
3. Spend $600 extra and upgrade to an all 9 system.

I hear Filemaker removed some features on the basic server 9 compared to 
server 8.

Stublito