I am with beryld on this. Most people have a problum with more than 2 or 3 higher end models in a render BUT if you do it in layers there is no problum rendering them one at a time then saving each one as a PNG . You can save each model as a PZ3 to bring in ( Import ) an make the changes you need and its certainly easyer to work with one model at a time then 3 or more.