Ive got both the 17-55mm f2.8 & 70-200 f2.8. I do find that the focusing on the 70-200 is faster even though both are f2.8. Guess latest technology plays a big role. Hence if u can afford, save for the latest tech. Weight is a concern initially. I do hit the gym quite often and hence thought that this 70-200f2.8 shouldn't be a prob for me until I carry and wear it on my neck. Very, very siong. Nevertheless I bot the sun sniper strap recently and the prob is resolved. It can hang on to my body the whole day and I dont feel any strain at all. The other 2 popular alt will be Luma Loop and Black Rapid. Many gd comments also. Hope this info helps.