I've used ATI cards, but never owned them in my own systems, so I am not a fan.
I've had a LIAN-LI case and was very impressed, but that case looks a lot bigger and uglier than the Cosmos S, also I am not sure about the silence factor, which is important.
I think I will swap the HDD for a VelociRaptor 300GB, it is correct to think that the HDD is weak. I'll also NOT get that monitor.
Motherboards? As far as I've seen the ASUS is the best of them all, loads of features nad a good cooling system.