I remember reading about the Sega arcade game Daytona USA. Instead of back to front or front to back rendering, it was a mixture of most important (your car, race track) to least important (background stands, trees, etc). It included a hardware watchdog that would trigger the next frame even if the current frame was not finished rendering, to guarantee a constant 60fps always. For an immersive experience, it was more important to keep the frame rate constant than it was to render every polygon.