As many Google adsense publishers looking for more large ad size to optimize their blog or website more profitably, and advertisers were also looking to promote their products with large banners to get more clients. Google takes these requests positively and announced two new ad sizes on June 3rd 2014.
If you blog has huge space in header then you should try 970×250 ad banner, it may increase your adsense revenue as per my experiment but as you know its totally depends on your blog niche and layout. For this ad size you can chose text and rich media ads both, before try we recommend you to customize your blog header to place this sized more creatively.
According to my experience most of us gonna try this ad because we all have good space in out sidebar but still its also need little but customization to adjust between your social bookmarks.
You are not allowed to place more than 1 ad of these sizes and as usual you have to follow Google adsense policy and guideline