do choice mats really give higher craft exp than fine? I've personally never noticed it, if it happens the difference is miniscule and lost in the degrades that are inevitable when overcrafting. The only real difference I've seen is the price you get for the item from the npc merchants.

Needs checking, maybe it was true in the past but isn't the case at present.

Crafting with Choice versus Fine has nothing to do with overcrafting. The quality of the materials (Supreme, Excellent, Choice, Fine or Basic) determines what the stats will be like for the item. Better quality items give better stats.

Overcrafting is the practice of crafting beyond your crafitng ability for that type - if you get up to level 120 in light armor and your heavy armor crafting is at level 101, you can still craft heavy armor at the level 130 possible because of your light armor level, you will just suffer more failures and partial failures.