I have an XT with the kit lens and a 50mm f/1.8 right now. I'm still learning so I can't justify replacing the kit lens yet, but I would like to extend my range a bit so I'm looking at the 70-300IS and the 70-200 f/4L. What do you guys think about these two? For around the same price I COULD have L glass but at the same time I get an extra 100mm and IS with the other, so I'm leaning that way. Opinions?