7200 rpm is better. Cache size is largely irrelevant.
Caan you manage a SSD? It absolutely transforms your laptop.
Assuming a SSD replacement would cost too much, consider the seagate momentus XT 500gb drive which has a 4gb nand cache which will give you ssd performance for the things you do most.http://www.newegg.com/Product/Product.aspx?Item=N82E16822148704