im trying to order 1gb ram upgrade for my new imac, but the config thingy on crucial says i could have either the 4200 or 5400, but im not sure what ram is in mine, ive had a search and people say to use crucial because the imac is fussy, but im none the wiser and want to match the speed of the existing one, i dont want to pay for the 5400 if its only 4200 in there already.