I bought a Ring of Extreme Wielding that boosts one handed 35%. If I disenchant it will I be able to create an item of equivalent strength (depending on my enchanting/smithing/potions, of course). I'm not at 100 on anything yet so would I just kill the ring and be stuck making 20% boost or lower items?

I don't think you would be able to make anything as powerful as that if you aren't a high level in Enchanting and with the right perks. I would check various merchants or chests until you find one that is only like 15% and Disenchant that.

The base magnitude for one handed enchanting (0 skill, no perks, grand soul gem) is 13%. So, in effect, your enchanting skills/perks/potions would have to allow for almost a 200% improvement over the base. You can test your capabilities with any skill related improvement at the enchanting table: the improvement rate it shows when you select an enchant always shows the base rate, then use a grand soul gem to test any skill enchant on an item and see what improvement you actually get over base (you don't have to actually create the item if you don't want to).

That's true. What's more you can always just save the game before you DE your ring and if you can't make one as powerful you can just reload the save. But to get a 35% I think you need some of the best enchanting gear possible, plus the right perks and 100 Enchanting, and a good fortify Enchant Potion.

The % of the Enchant is not taken into account when Disenchanting item. If you find something with Fortify One-Hand 15% or 35% and Disenchant it, they both give you the ability to perform Fortify One-Handed Enchants on items. When you Enchant items, your Enchanting Skill and Perks are taken into consideration along with the Soul Gem type you are using and what Soul is in it. So you can disenchant that 35%, but unless you have a high Enchant Skill and the Perks you are going to only be able to do a pathetic %.

The size of the enchantment on the item has no bearing on the size of the enchantment that you can do. So there is no difference between what you will be able to create after you have disenchanted either a 35% item or a 15% item. It's all dependant upon your skill level, your perks, and your boosts, such as potions.

I'm pretty sure without using the potion loop to create super potions and enchants, the highest that enchant % can get to( for fortify alchemy or smithing) is 29%-32%. Your almost better off keeping the 35% ring that you have, get one thats like 15% and disenchant the lower %. Then just complement the 35% with one or two others that you created.

Yes, but the BM (base magnitude) for Alchemy and Smithing are only 08%. So even a 200% over BM for those is only going to get you a 24% enchant. That 32% enchant for those skills means 300% over BM, and for 1-H would mean a 52% enchant.