Benchmarks, and finding out which cards are newer.
The easiest way to evaluate whether one thing is better than another is by using benchmarks.
One good site is VideocardBenchmark.net where performance figures can give you a rough idea of whether one card performs better than another.
The other factor is how old the card is. Newer cards support newer features but an older card may still be higher on the benchmark but not support the same features required by your program such as DirectX 12.
So you are looking for a card on that benchmark list that is higher and newer than a GTX 970, or higher and newer than an R9 290. They are both pretty high end cards.
That website also lets you compare cards thusly: http://www.videocardbenchmark.net/compare.php?cmp%5B%5D=2719&cmp%5B%5D=3533
As you can see the RX480 performs slightly better than the R9 290, is newer, supports the same or better features and has a significantly lower power draw which is probably the main benefit.
That card would be fine.