for a drive that contains windows and where your programs and games are installed you WILL notice the difference.
Windows, Programs & Games will take noticeably longer to load
As a data drive for movies, music & such there you would not notice the difference unless you are moving large amounds of data around regulary.
5400rpm drives are generally limited to laptops now.
5400 died out in 3.5" drives for a good few years (40gb onwards really)
there has been a revival and 5900 rpm 3.5" high capacity drives have been quite popular