I did some renders last night with both P5's Firefly renderer, and the old P4 renderer, just to see what the difference is. Though the P4 render might be faster, it doesn't hold a candle to the Firefly render engine's raytracing, distortion maps, reflective surfaces, motion blur, etc. Add in the materials room, and you can get gorgeous effects not possible with the P4 engine. I always use the Firefly engine for rendering, even drafts.