Or render at slightly less (4500 px wide or so) and enlarge 150% using OnOne's Genuine Fractals or so. It interprets extra pixels where it's needed, and keeps sharp edges sharp. Works really good, very much better than PS. I used it for a TG render at 4400 px wide, which will be blown up for an exhibition at 2 meters wide. I haven't seen the result yet, but on screen it looks quite ok. And, as Matt says; you won't get your nose touching the print anyway. It was Rembrandt who said after some criticism on his rough way of painting; don't get too close to the paint, it might be poisonous.