Own them both. Great boots! With that said, here is my thoughts on the ones I have.
Salewa - Mountain Trainer GTX - They come with the "no blister" guarantee so thats a hell of a return policy. The fit is a little narrow for me, so good for you. The 3F system they have on their boots is fantastic. This is the metal piece running around the heal. It helps to really lock your ankle and heal into place and this is where the no blister guarantee comes from. I would say, if you have a narrow foot your in luck with Salewa. I have a slighty wide foot so the heal fit fine but right at the pinky toe I just couldn't get an exact fit. They are good and comfortable but don't fit like a glove. No stitching issues, broken lace hoops or Gortex issues and have 150+ miles on them. One things tho, never a fan of the step plate on mountaineering soles. That dumb flat part of the sole on the outside of the toe box area. But thats just me.
Zamberlan - 760 Steep GT's - Best general hiking boot I've ever worn. Zamberlan has been around for 80+ years and have really learned how to make a great boot. The Steeps fit a little bigger then normal fit. I normally wear an 11 but the 10.5 fits me perfectly. Zamberlan also run a tad wider then most normal boots. This is due to the toe box design that they have. Don't worry, not like the weird horrible Crispi incline toe box. The sole, stitching and really the whole boot have treated me beyond great and 200+ miles on these boots. If I'm on a trail these are on my feet.
Zamberlan - 960 Guide GT - This boot has the same fit characteristics of the Steep but its a tank. The comfortable Nabuk tops really wore in nicely in about 20 miles or so. The 3/4 rubber rand has a great seal with the leather upper and haven' had one separation point, even at the natural bend point of the boot. The sole is about the exact same on these boots as the Steeps too. Vibram Soles and they you Zamberlan, plastic toe tips. Big difference in the Guide is its a single piece of Nabuk leather upper and not stitched like the other Zamberlan boots.
Hope this helps man