I have the "bargain basement" 70-200 f/4 (non-IS). I have no regret at all that I don't have the IS, 2.8, or 2.8 IS incarnations. Why? Because firstly I could afford it, so am comparatively much better off. Secondly, and mainly because I have no need for the extra stop, size and weight that the 2.8 offers. That would be like going out to buy a small car to get you from a-b and then regretting not buying a truck. Sure the truck would also get you from a-b, but it's much bigger and heavier, and the extra functionality it offers is not needed.