I'd pick up something to cover the lower end of the spectrum, and then go with another lens to cover the upper end. I use a Tamron 70-300mm on my *istDL, and although a bit slow (5.6 @ 300mm) it take nice pics. I picked it up for $90 shipped off eBay. (Example Pictures)
I just bought a 35 F1.4L and sent it back to B&H. I thought I wanted one after having rented one but the new copy I received wasn't as sharp at F1.4 as I wanted for $1120. Besides, my EFS 17-55 @ 35mm / F2.8 is pretty much as sharp as the 35L @ F2.8.
Here is a EFS 17-55 versus EF 35 F1.4L comparison: LINK
Top Row: EFS 17-55 @ 35mm at F2.8, F4.0, F5.6
Bottom Row: EF 35 F1.4L @ F1.4, F1.8, F2.8, F4.0, F5.6