Or the wait, don't forget about the wait.
When I bought my m505x (it was a Saturday), I needed the notebook on the following Monday. I probably would have ordered an XL, but because I took my sweet time choosing a notebook, I was left in time crunch. It was kind of nice to be able to walk into the Gateway Country Store and walk out with my notebook. Plus, they let me check for dead pixles.
I have a DVD burner in my desktop, I can get copies of XP Pro from a friend at MS, and I have a fairly highend desktop with a 9800 Pro. So, I think the trade off between the X and XL was pretty small. If the XL came with a 7200 RPM drive, I probably would have chosen it over the X.
However, if you think the XL is the one for you, I would get it. That's the nice thing about having 2 models to choose from.