is there that much difference in speed/reliability between the two?
i could just buy another 500GB when the need arise and if so do you have to reinstall the OS when setting up a raid array?
what raid array is best for 2 caviar black 500GB's?
1) The 1tb drive will actually be a bit faster with the data(like the OS) that will be initially loaded. The outer rings are faster because they are denser. That gives faster transfer rates and shorter seek times for the initially loaded data. For the extra $10, I think it is very much worth it.
2) What do you want raid for? And, what type--raid-0, raid-1, or???