I have a 5DmkII with a 24-105L. mostly shoot outdoors , and mostly not fast moving objects. I have a demanding day job , but find things to shoot to/from work, and weekends. I was planning to get a 70-200 f2.8 , works well with TC ( not sure I can afford IS version) But having second thoughts. a 100-400 f4.5-5.6 is slower, pretty bulky, but has great range and no overlap with the 24-105. a bit concerned with the speed. another interesting possibility is a 180 f3.5 L macro. I've read reviews, relatively slow AF , but very sharp, and outstanding macro. could even work with a 1.4 TC But could it be a practical lens for landscape and general purpose. not able to rent this lens locally, otherwise I'd try it. I'd love to hear from folks have real world experience with these lenses.