That's a 24w margin of error :D but yes of course Wiggins isn't going to be able to do 56km at sea level. Bobridge's IP world record was done in crazy high heat which you can't scale up for a 1hr effort as you'd just die off after 25-30min.
Bobridge was still the fastest IP rider in a UCI legal/non-superman position, behind Boardman before he got Boardman's record so it wasn't just a fluke.
Boardman reckons 53-54k for Brad.