Well your card is better than your brothers and it shows just what the difference is between the GTX 670 and the AMD HD 6970 are.
The first link is the difference between your two cards. The other links shows the scores for benchmarking. I hope this helps and good luck to you both.
670 vs 6970http://www.anandtech.com/bench/Product/598?vs=509http://www.graphicscardbenchmarks.com/page/graphshttp://www.graphicscardbenchmarks.com/page/table