My Nikon D200 uses a Nikkor 18-200 mm lens. It generally does great with auto white balance, but I need something for scheduled shoots to help me with WB. I'm a NAPP member, so I'm quite familiar with the WhiBal card and the ExpoDisc filter (almost every issue of Photoshop User magazine has full-page ads for both of these products). If you were limited to one of the two products, which would you get? I should note that I don't mind taking the time to correct my images in post-production. Thanks.