Just returned from a week of backpacking in Canyonlands and took a new 100-400 II instead of the 70-200 II so I could cut down on lenses (took the 24-70II, 24 TSII and the 100-400). I'm pleased with the IQ and portability. IS was great for off tripod wildlife stalking and performance on tripod for HDR landscape was wonderful as well. Here's a shot of a ground squirrel with the 1.4XIII, 5DMK III, ISO 1250, 1/800, f 9 (processed in DPP4 from a ca. 2400 pix crop). This lens plus the 24-70 II and the 1.4X III covers a lot of perspectives (just needed the 11-24mm to complete the kit).