The vision sides with S4 are never permanent, but I would t recommend exceeding 100mg per day. Once you go beyond that, the returns diminish significantly but the side effects continue to go up at the same rate. For me, I have found 100mg to be extremely effective without side effects getting too bad.
This is a great post and is true for many compounds. There is a point of diminishing returns and honestly, that point is usually bordering abuse of the substance. IMO, Run it at a reasonable dosage that is effective and nothing more