Tip for upgrading armor/weapons (helps TONS with special armor and weapons, such as Nightingale)
Enchant a necklace, ring, bracers, and hood/helmet with Fortify Smithing (only ones you can put that enchantment on). I just used a gold necklace, silver ring, and leather gauntlets and helmet, cheaper and lighter the better since it will only be for this purpose. This will give you at least 32% better (depends on your Enchantment skill) as long as you use black soul gems to enchant with. Then, find a Blacksmith's Elixir, which gives you an extra 50% smithing for 30 seconds.
Equipping all your smithing fortification items and then using the Blacksmith's Elixir right before you upgrade weapons/armor will give you whatever percent you have in Enchantments above your current level (which should be at 100 to get any use out of this), and then 50% of your overall level on top. Using this method I was even able to upgrade my Daedric weapons, which were already Legendary, another 20-30% in damage. My Nightingale armor was upgraded from Flawless to Legendary as well.