no clue what the HD501JL is but i have a P7K500 in my server... only reason i have it is becasue bestbuy had a deal on a simpletech 500gb external hd for 40 bucks... i bought it, took the hd out to put in my server.
I personally wouldnt go outta my way to buy a P7K500. its a 250gb platter drive but has very slowed down head movements to make seeks no louder than idle and to reduce power (almost like a WD green power drive, but the hitachi spins at 7200rpms) problem with slowing down the head movements is random access time goes up.. upwards of 18ms.
Honestly id rather go with a 500gb -640gb drive from WD or seagate.