Just for comparison:
I rendered the scene http://www.renderosity.com/mod/gallery/index.php?image_id=1676006
in 1600x1200, at 300dpi (not the one posted here, I did this higher definition render later) and, despite all the vegetation (750,000 plant instances and 25 billion polys), water reflections and transparency, it rendered in 5 hours, in a quadcore.