I have never used mental ray..... For the most part i try and keep my mesh as clean as i can with quads but some times no matter what you need a few tris in there to get the shape you need ......

Most of my models are pretty easy to see where the 3 sided faces are and i'll go in there and move edges around adding edges wiht split poly to get a 4 sided face.

As far as exporting and that i just select my mesh and export the mesh out unclicking channels, history ETC in the option box.. seems to do the trick for me. Then just import into a new scene.