jerold222 wrote:
You have to ask yourself, how is the image quality of the canon lens? If it is good to excellent, there is no need to up grade.
You don't say what camera you are using, a full frame or a crop sensor or how you are using it, hand held or tripod.
Image stabilization at 200 mm is not really beneficial compared to Good shooting habits. even at the cropped 320 mm is still of limited benefit.
Many people still recommend non IS lens in the lower range lenses.