Being realistic and practical and considering budget, just about any lens will perform adequately shooting at f/8 and mid-way through its zoom range where the image is conentrated in the highest quality area of the glass. The 17-85mm already has a lot more scope than a 10-22mm or 17-40mm lens based on focal length alone.
It's usually when you shoot wide apertures (towards f/2.8) or stopped down (~f/16 and upwards) and at the extremities of the zoom range, that lenses really start reveal their inherent flaws.
That's when quality 'fast' glass comes into its own, with improved faster focussing - not much of a requirement for landscapes in my opinion, as well as performing better at the extremities of the zoom range.
So if you're already noticing its flaws then do upgrade.
Careful though - one upgrade tends to lead to another.
None of the suggested lenses will replace the focal range you have, and once you get used to f/2.8 you'll want to buy more ... and more.... and more lenses!!!!!!