Being the quirky type, I have to take up the gauntlet on this one (not that there isn't a lot of bad english around these days!):
Actually, "impacted" is the better word to use here, since we're talking about a detrimental performance difference - and ,when not used as a verb - like an asteroid hitting something, "impacted" carries more of a negative connotation than "affected". Think about it - when the dentist tells you your wisdom teeth are trapped below the gums, he calls them "impacted"; not "affected". "Affected" has more of a connotation of "change" or a relative comparison between multiple things. This was a directed comment about the detrimental performance of a particular object - hence "impacted".
--Noel "HB" Wade