While IS may not stop things in motion, it allows you to shoot at slower shutter speeds that will still freeze relatively slow moving objects in sStreet portraits but would normally blur due to hand shake.


Rule of thumb is you shutter speed should be 1/(focal length)to avoid hand shake blurring. So at 200mm you would need at least 1/200. With IS you could probably shoot at 1/60(?) and still freeze your subject pretty well and not experience blurring from hand shake.


I owned the 70-200 4.0 non IS and I hardly used it. At that focal length w/o IS. I couldn't find too many uses for unless it was studio portrait with strobe lighting or outdoor sports on bright days. So I sold that with in a year of purchase.


So for discretion and value I'd say 4.0 IS.