here is something i did at work for an event. if you go to the HMI 2005 in hannover (big joke saying this in english) you can see it at 2,70x2,36 meters.

took around 27 hours to render (6378 x 5575 pixels) and 4 hours of photoshop finetunings
ugh i even used blurred reflections which are faded that much. on a 2x3GHz 1Gb Ram. well thats not fast;)