Thanks for the replies. My bad- I meant my SRAM cassette, not hub

Budget... would like to stay around or under $600, but if I realistically cannot get anything in that price range that would be a decent upgrade from the R500's I could always save my money and work on improving the "engine" before upgrading. Also, if it makes any difference in a few months I plan (I'm determined) to be down around 180 lbs and maintain that weight.