I'll advocate using Troll over Bronze all day, but yeah.. I'm gonna have to agree, go with Iron.

I'm not even at that point in the game yet since my H&H world (I just killed Elder last night and am preparing heavily for the Swamp before entering, including building a new base on the closest Meadows to a decent-sized Swamp biome on my map), and yeah.. I'd say go for Iron as soon as you can make and fully upgrade it.

So I guess, use the Troll stuff until you have all of the materials you need for everything Iron you want, including max upgrades (whether you can fully upgrade them right now or not), then go back up with it.

From what I've seen of the Mountains it looks like it is definitely not friendly for running/jumping around very much, so I'd say the movement speed penalty, if there is one for Iron armor, would be acceptable based on the sheer defense upgrade.