I'm about to order my first Dish dvr and am looking at the 501 and 508 refurbished models at dishstore.net Is the 508 worth the extra $70? I don't like the idea of not being able to upgrade the hard drive but figure if I get the 501 it will be good enough as I will just transfer the shows to dvd or my pc hard drive if I am running out of space. Just wondering which one you guys would choose.