Update only modified fields in Entity Framework
Why bother checking if the value/property has been changed? You are just adding additional complexity for no reason. Sure, it might be slightly! faster to only update modified values, but in return you are adding an overhead to keep track of the modified values, which will diminish whatever performance boost you got. 

Just invoke Update on the entire object... All values that has not been changed will remain the same and the values that has been modified will, well, update.

If it's speed you're looking for you are most likely looking at the wrong place to squeeze ms from.