With a $600 budget you could probably squeeze a better card into your build. I recommend taking a look at Logical Increments, Choose My PC, and /r/buildapc. PC Part Picker is also a great resource, but with a different purpose.
I wouldn't be concerned about getting an AMD card vs. an Nvidia card. Nowadays, they're nearly equivalent. Higher end AMD cards (7850 and up) are pretty overpriced right now because they're better for cryptocurrency mining, creating huge, insatiable demand for them (I had to get an Nvidia card as a result).