Not to mention the fact, that when Chael fought Anderson (Silva injured or not), Chael was a BEAST. He handled two solid guys with ease, two guys I highly doubt GSP would manhandle in such a manner.
Only other times I've seen Silva controlled and put on his back for long periods, was in a ring and when he was a lot younger and thinner.
GSP harder to beat at Welter, but at middle, I would have to go with Anderson.
Think I would be more interested to see Jacare or Lombard in there with Silva. If (and probably once) GSP get's past Shields, then throw him in there with Silva also.