I have the 17-85 IS. It only has the 1-mode image stabilizing, that helps with camera shake. I know this won't help when panning, but would it actually have a negative effect when panning? I mean, is it best to turn off the IS when using it to pan with a race car? At one point, I looked back through photos I took with this lens, and they all seemed a bit OOF or blurry of some sort. The shutter speed was ok, but I wondered if maybe I forgot and left IS on, having a bad effect... Any ideas?