I never really did figure out the differences in hdd's. I have 2 of the 1TB barracudas(for 5 years now) and I've never had a single problem with them. On the other hand, in the past year my brother has gone through 3 different Caviar blacks. I just find it that seagate is the most reliable.
I would go with the ASUS gfx card. They're products are very reliable in my memory.
I have the Ripjaw ram, wouldn't say it's better or worse than any other ram. it's hard to tell the difference with it.
I dont know if it's changed any since my graphics card, which requires a 700w power supply under load, but you may want to think about upgrading from the 675w.