h50 is old skool.. if you don't already have it, get something else. If you have the h50, buy a 240 rad and mod the h50 to work with it, you'll be much happier. With the H100I hovering around the $100 price point, it makes the h50 look like a waste of time.
Will it keep your cpu cool over 4ghz? Sure, but how high do you want to go and do you want to be limited by your cooling?