If possible I would get a real long arm an Innova 22 inch or Innova 26 inch on a 12 foot table.
http://innovalongarm.com/
I have a Janome 6500 and love it but it is not the same as a long arm. I would rather have a more simple sewing machine and save the money for a real long arm. If I could not have the real long arm I would go for the biggest opening and get the Janome 7700. You'd have lots of fun on it and you can use it to quilt full size quilts sitting down and moving the quilt around on the machine.