The 980 is an enthusiast graphics card meaning you’re paying top dollar for the prestige of owning one. It undoubtedly performs better but it’s completely unnecessary if you’re working inside a budget of any kind as you’re not getting the best bang for your buck.
The 970 is the best value of any card on the market and will future proof your system for at least 4 years. You can get one for $320 and can get 60 FPS in almost any modern game at ultra settings as long as you’re at 1080p. There’s a reason the market went into a fervor at the announcement of the 970 and the card had been sold out for almost two months before supplies finally starting settling. If you get a 980 instead of a 970 keep in mind you get a 15-20% performance gain between the two, but the 980 is 30% more expensive.
A 760 will probably need to be upgraded in 2 years due to it’s 2GB VRAM. The majority of projects (and games) are now going to be aiming to work with the 8GB VRAM of the PS4 and you’re suddenly going to find yourself having trouble juggling all the textures in your games. The price is right if you’re okay with reselling your 760 in 2 years and upgrading again. But buying a 970 for $100 more will get you a card that will last you for another 2 years. Is the $100 extra worth the peace of mind (and performance)? For me it is. But we don’t know your budget situation.