Thanks, jon, I hadn't thought of that being a factor. One thing which I've found helps in P6 is to go into the Materials Room and go a bit indirect on the background. Set up the standard background color node as white, and then feed an ordinary Image Map into the color channel of that node. Don't use a Background Image node. That probably still has texture-size limits on resolution, but it gets around the distortion and awkward margins, and it's worked well for my web-resolution images. Background props in general can also work better by using Ambient Color instead of Diffuse -- it avoids shadows cast by foreground objects.