I assume you are doing this for franchise mode? I honestly think you should give him like a 93ish or so rating ovr from the original Madden '10 roster.
Why? Say next season, assuming there is one, Plaxico Burress becomes the comeback player of the year, has 1,253 yds recieving and 15 TDs. A Mike Vick type season, if you will.
Here's where your problem comes in: While you're watching Plaxico Burress have an All-Pro, comeback player of the year season, you won't be able to replicate his success in your franchise, because he's a 70 ovr.
I'd rather overrate the guy than risk the chance of underrating him.