Go with 2.0. And its because they over judge what you need for a PSU, this is to cover all their bases. Maybe you have 10 hard drives, or maybe you like to overclock, or maybe your PSU sucks. They don't want to say you can get a 300w PSU and then it not be enough.
But that card only draws power from the PCI-e slot, it litterally can't consume more then 75w of power.
You should be fine.http://www.tomshardware.com/reviews/radeon-hd-5670,2533-17.html
At peak performance the system only drew 76w of power with that card and a more power hungry CPU.