I've blown Xpan scans up to A3+ (19" length) with good results. The files from the scanner need a little work with contrast and sharpening but the info is there. I seem to have better results with transparencies than color negatives, might just be me.
Have done a few 6x6 negatives and generally happy with the result, with Acros 100 could get film grain as the limiting factor for sharpness, again need to work with the scanner file for contrast and a bit of sharpening.
My flickr page has an Xpan set, all the images were scanned on the V500 and processed in Aperture.