Mr. Mister said:About the RAM heatsinks: Apple does this solely to keep it quiet so the heat can dissipate with minimal prerequisite airflow and thus minimal noise from the fans. You can put any RAM provided that it fits the memory interface spec, but the Mac Pro will detect increased temperature and run the fans a bit faster.
Just an FYI. The heatsinks aren't an Apple thing. They are Nanya thing (ram manufacuter). Apple may have chosen them because of this, but this isn't something Apple has done.