I think the problem is going to be that there are no longer enough preferred loops left to meet the needs, the 300 loop is the only preferred pet loop left as far as I can figure.
Having said that, when we went in December I had a year old ressie for a preferred site and loop 300 recorded on the confirmation. When we got there we were told that the 300 was full and we were assigned a site in the 700 (at preferred rate) We were not happy and arranged that we could move in a couple of days when a site opened in the 300. After we got set up and looked around we fell in love with the 700 loop. It has a great pet walk, not too far to the pet park, close to the settlement and nice big sites. We ended up not moving!
I have a preferred site booked for April and I have requested the 700 so we will see what happens.