I am trying to acquire only those lenses that are integral for a good semi-professional wedding/portrait photographer. I have about $700, and thinking about buying Canon 50mm 1.8 + 70-200mm f/4 L = $700. I know 2.8 L is the best out there, but I can not afford it. Saving-up is not an option in the forseeable future. I can afford the f/4, but don't want to regret buying it. My questions are: 1. How much of a difference is there b/w these two? How much more useful is 2.8 over 4? 2. I will also have to get the non IS version f/4. Does this make the lens pretty much useless? 3. Are there any other L lenses out there that are $600 and better than the 70-200 f4 L? (By "better", I mean the general lens quality for someone building-up their photo equipment collection). Thank you.