I'd be getting 8Gigs of DDR3. And I don't think any Intel Ivy Bridge chipsets support DDR3 Mem anymore..
I've got the 3570k and the EVGA 660 SC, and so far, everything that has been thrown at it, it has destroyed.
The 660 is a bit better than the 7870 and a bit more expensive.
Make sure the motherboard you get will support sata iii too, there's no such thing as futureproofing a computer, but that is a start.