To eliminate the banding, you need to pre-process the images to correct the darkening at the edges. You might be able to do this with the vignetting correction in the the Adobe RAW converter or Filter->istort->Lens correction. Otherwise, you could make a mask to selectively brighten the edges in Photoshop, possibly based on a photo taken of a blank white sheet of paper. Best to do such adjustments in 16bit mode to avoid posterization banding. The PTGui Pro stitcher has a vignetting correction option, so you could try downloading the trial version of that.