TG, BB's Envsphere sky images look best if you decrease your camera's focal length between 20 - 25 mm.  You would be increasing more lense coverage due to the wide angle nature, making the background image sharper.  The down-side is you must bring your camera closer to your subject where it could be influenced by wide angle distortions.  Also, there is gamma correction present which must be reset to 1 if using render Gc.