Go for instant gratification. I have both and even though I've had my 70-200mm f/2.8 IS for a couple of years, I still like to use the 70-200mm f/4 non-IS. Why? Because it is lighter and therefore easier to carry on long hikes and if you don't specifically need the wider aperture and can use a tripod or monopod, it produces beautiful pictures that easily equal those from the more expensive lens.