Dude if your running a 920 x58 system you would be nuts to think that SB is going to be any kind of noticeably faster....your going from a highline system to a mainstream system...wanna upgrade wait for socket 2011 in the 4th qtr....x58 to 1155 is a sideways slide..hesitant to call it an upgrade.....
unless money is plentiful and your looking for something to do forget this swap.....