anyone have some experience with either the canon 1.4 or 2x extender? I was looking at buying a new 40d to replace my 20d, but I feel i need lenses before a new body. I'm going to hawaii shortly and would love to photograph the surfers in action. I was thinking about picking up the 70-200 2.8 IS lens in place of the 40d and was just curious about the extenders. the reviews on b&h went both ways on the 2x...I'd prefer this one over the 1.4. I dont mind losing two stops but I'm worried image quality won't be as sharp with it. anybody use it firsthand and have some input?