In reply to GwilymR:
I have a Tamron 18-200 on my 350D and I see in old reviews of it online that it was well rated as a do all, go to, walk around lens - which is pretty much why I bought it at the time, as well as not wanting to change lenses in climbing situations.
But pretty much from word go anything near the 200 end was simply not good enough and no tripod or workarounds helped. So I would not try and cram that much into a lens again, as I probably never use over 140 or so.
I'm doing my annual will I or won't I upgrade DPreview trawling and thinking I won't go over 105 on whatever I get. I have reasons why I could use 300+ but not sure it's worth the faff in actual mountain use.