In reply to Robin Woodward:
When it boils down to it, you can have light or strong. If very lucky/rich, light enough and strong enough is do-able - but strong still equals heavy in most mountain applications.
If it's gong to be carried a lot and used in general mountain conditions, then the equation favours lighter and something like the T20 is a good choice. If however you really need extreme weather protection, exposed sites, torrential rain and hurricane force winds then (a) good luck and (b) heavy wins out, and you just get fitter lugging it around. The same is also true for longevity, particularly the groundsheet strength - certainly a plus point in the Macpac tents (you should see some of our plants...).
good luck
b