Interesting read. I think it may come down to personality and opportunity, rather than anything purely technical. I love IS and I wouldn't be without it, but I think of photography as a probability game. Anything that improves my chances of getting that great photo is good and I find that IS greatly improves those chances for wildlife. I use a 300/f2.8 usually with a 2x extender, which I can hand hold. If I had a heavier lens, the IS would be of less value as I would need a tripod anyway.