Mike,
If you are planning on staying with 1.6 sensors, I'd go for the 10-22. Its next on my list as it produces near 'L' results.
I've had both the 17-40 & the 24-105 and can't say I was really impressed by either. Both were too soft wide open. The 17-40 was OK but could show an alarming amount of CA if not pointed just right (the 16-35 is
much better).
I found the 24-105 soft as a very soft thing and also prone to CA though not as badly as the 17-40. Mine was an early example and the problem has supposedly been sorted long since.
Depending on how you like your landscapes, I wouldn't worry too much - I happily use my 300 2.8L sometimes. Even one a local award for "Best Landscape" with it!
But as always, if you can, "Try before you buy"! Any reputable dealer should alow you to take comparrison shots.
Good luck,
Peter