is there a difference

Solution
Look at some benchmarks, there is. 980 is about 10-15% better than 970, but costs 50-60% extra, not the best value for money against 970, which can max out games on FHD or 2k. You'd need SLI setup for tri monitor or 4k anyways, I'd save my money to go with 970, but if you can afford, 980 is obviously better. Another option is SLI 970s, which'd throw a single 980 out of the water.
10% only. Go for GTX 970

perfrel_1920.gif
 
Look at some benchmarks, there is. 980 is about 10-15% better than 970, but costs 50-60% extra, not the best value for money against 970, which can max out games on FHD or 2k. You'd need SLI setup for tri monitor or 4k anyways, I'd save my money to go with 970, but if you can afford, 980 is obviously better. Another option is SLI 970s, which'd throw a single 980 out of the water.
 
Solution