About the lightness: For example in the '93 Klein catalog, a bike with Suntour XC Pro MD was over 2.2 lbs lighter than XT and 1.3 lbs lighter than XTR equivalent. So Suntour did some pretty impressive stuff back then.
Suntour has more sex appeal but XT is just so damn dependable. If you are restoring a bike for show do the Suntour if you are gonna ride the retro bike as your main mtb go Shimano. But thats just my opinion.