Initial reaction would be a Mayweather decision but Vernon is a lot bigger than Floyd, and despite his age the man can box. There's nothing Mayweather does that Vernon doesn't do equally well. Vernon Forrest is a freak of nature, as is Mayweather.
Still, I have to go with the knee-jerk reaction for a Mayweather decision. 116-112, or 115-113. It would be close.
If it were a prime Forrest I'd go with a Forrest victory. But you have to take into account the condition of his shoulder.
Floyd was only 150 lbs on fight night against ODLH, he can't get much bigger.Forest has reach and heigh advantage and can get up to 165 on fight night.