don't get a 660, only 660ti if you were.
Get the 7870 it will be fine.
750w can even be called overkill for that rig, a 550-600 would be more than enough.
Extra ram is not needed unless extreme multitasking is going on and you run 30 applications at once. I struggle to use up my 8gb.
Vertex4 or intel 520 128gb SSD's are very good choices
Also, what is your budget for all this?