This is the MTB that I've ridden on numerous 100 mile rides, note the tires:
http://i17.tinypic.com/5x8flo1.jpg
Dressed down like this means the weather is good. When the weather is crap, it looks like this, but maybe with a single Ortieb on the back:
http://i18.tinypic.com/4zu6a85.jpg

In good weather, head up, feeling great, it takes about 7 hours to go 160kms. Bad weather, head down, cursing and wishing I were somewhre else, about 7.75 or 8 hours.

On my Trek 520, fendered, with a single Ortlieb, about 6.5 hours, with ease.
On my Sequoia Elite, with a 5lb bar bag, an easy 6 even.

I'm not your average rider, whatever that is anyway. I'm 51, and I weight 235 at 6', and I'm pretty strong as far as stamina is concerned.