For example, fortify barter or an enchanted item.

No, has used alchemy gear who took my alchemy far over 100 with no visible slowdown.

However in Oblivion powers slowed down skill increase as they set the base value and did not just fortified it. The skeleton key is most known for this. Not sure if this problem exist in Skyrim but it should not affect potions or normal enchants.

While I was wearing gloves/armor/ring/amulet of fortify smithing I didn't see anything slowed down at all on my way to 100.

I read somewhere it actually speeds up the leveling progress, because you do more (dmg, gold from potions, etc...) at lower lvls. Cannot confirm this with a source though.

It probably does for alchemy as expensive potions give more xp and good gear can raise your skill more than 100 points.
Not for smithing as the skill gain is the same for everything.
not sure if damage matter for weapons or it's just number of hits.

This is true for alchemy and speech, because your gain is based on the item's value. Pickpocket is also based on item value, but the value isn't increased with higher skill.


Smithing increases at the same rate regardless of the item's value (hence the iron dagger debate). Damage doesn't affect your weapon skill gain, but damage taken does increase your armor skill gain.