The formula for enchanting apparel is
net magnitude = base magnitude * soul multiplier * skill multiplier *
(1 + Enchanter perk) * (1 + specific perk modifier)
skill multiplier = 1 + 0.3 * ((skill - 10) / 100) ^ 2.
Therefore, the maximum magnitude (100 enchant, the appropriate perks, +32% Fortify Enchanting Potion) is:
skill multiplier = 1 + 0.3 * ((132 - 10) / 100) ^ 2 = 1.4465
net magnitude = base magnitude * 1 * 1.4465 * 2 * 1.25
= base magnitude * 3.6163
Regen Magicka's base magnitude is 20% and Fortify School's is 8%, so that means at best you should be able to add about 72% magicka regen or 29% fortify school to a single enchantment on one piece of equipment. With Extra Effect, you could add both to a helmet, armor and ring, and fortify school to a necklace, which brings you to +216% magicka regen and +116% fortify school, on your choice of apparel. That means you can reach the armor cap fairly easily, which equals 85% damage reduction.
The best stuff you can find would be something like the following:
Head: Morokei - +100% magicka regen (note that you would have to replace this for Mage Armor perks to work)
Ring: Ring of Peerless [School] - +25% fortify [school]
- or - Ring of Recovery - +100% magicka regen
Chest: Master Robes of [School] - +150% magicka regen, +22% fortify [school]
Neck: Necklace of Peerless Magicka - +70 magicka (AFAICT necklaces can be enchanted with Fortify [School] but generally aren't found as such)
So with the above equipment, you'd wind up +44% (or +144%) more magicka regen, -69% (or -94%) less fortify school, and +70% magicka and almost no armor rating. That may look comparable, especially given the tradeoffs in putting perk points in enchanting or anything else. But consider the following:
- The real benefits to armor become clear the more you have. That is, each additional point in armor adds more to physical durability than the previous point. With clothes equipped, you lose out on perks like Custom Fit/Well Fitted, Matching Set even if you get the best possible gauntlets and boots.
- A school fortified 100% (i.e. 0% magicka cost) is better than all the magicka regen out there for that particular school. Most mages focus on only a few schools, and there are benefits to concentrating.