there is a cap on the alchemy loop I believe, it starts giving you diminishing returns around 33% better potions on alchemy gear I believe, I dunno, ive never done the loop, but with the fortify restoration glitch you can make ridiculous enchantments, eventually you do hit a point where it flips over into the negatives, but I think thats not until you start hitting really high numbers.
Have never really experimented with fortify restoration glitch either, so this is just what ive read.