The biggest flame size I could get is about 40cm (there's a post with the subject "printing flame fractals" or something), but at 150 dpi - enough I think. I didn't print it that big yet, but on the screen it doesn't seem that it was too affected. I did a print in 300dpi of a flame in A4 size, and I think that if I had printed a 72dpi version of the same image, there wouldn't be much differences (the image is "Woosh"). For more "blurry" flames like "Woosh", it's possible to render them (actually export them) in 150dpi then try a little resampling in Photoshop to make them slightly bigger.