Thanks guys. I did look at the 15-30 from Tamron but the bulk puts me off. I know this may sound crazy but I'm really trying hard to reduce the weight of my bag for all sorts of reason, not least due to stricter air travel requirement and long hikes. I know very little about the 18-35 but it certainly looks like a strong contender in my book! I'd prefer 15/16mm wide but I think I might be able to live with 18. With any equipment, there's always a compromise somewhere.
Thanks for both your thoughts and suggestions.