My opinion is that's false economy, as a wise owl once told me, buy the cheapest possible camera with the best possible lens. If you get a lens that is not quite where you want to be, then it'll put you off buying an L Series. If you can find one and have the funds available, buy it. It also means you don't blame the tools, if you're getting sub standard photographs, it's you to blame and there are a variety of ways you can fix that (tuition etc).Would love a L lens, but I don't think my experience warrents such an expensive purchase yet.
If the lens just isn't sharp enough at the long end, or you have a slow lens, so are missing the action, then you will be looking for a new lens soon as your experience goes up.