Don't get dissuaded from buying 4K monitor. Prices are actually quite low now, especially on mainstream 4K@60Hz displays.
Got my 24" Samsung for just under $400 (now it's around $330-350). If you can afford it - get their newer "Quantum Dot" display:
https://www.newegg.com/Product/Product.aspx?Item=0JC-0007-00G95
When I first bought my U24E590D, I was still running GTX950 in my rig, so don't get sidetracked by "Titan XP" comments and other crap - you can always run games at lower resolution or lower settings on your 970. Even then my puny videocard gave me all the necessary horsepower to beat Alien Isolation in 2K and re-play all of my older games like Portal, HL2, all Borderlands and some other games in native 2160p.
I'm currently sporting a GTX1060 6GB and about 80% of my steam library is quite playable at 4K, so if you like pre-2014 games, then most of them will work on High or Ultra no problem. Newer AAA are a struggle, but you can always drop the resolution and tune settings to get your desired 60+FPS.
You can always upgrade your GPU later. New video cards are coming out almost every year, while monitors stay the same for a lo-o-ot longer.
Pros : The main benefit of migrating to 4K right away is productivity. simply browsing web, reading docs and working on it in general is a lot more pleasing and relaxing.
Cons : absolutely none.
Other Notes : font scaling on some software is not working right, but it's not a monitor's fault.
Also, Bill mentioned ultrawide monitors. Those are amazing, but only if you have enough desk space for one (and an extra $$$). In my case anything bigger than 27" is out of question, so I went with a traditional 16:9 monitor w/ higher pixel density on 24" panel. Prices on ultrawides are also higher than regular 16:9 2K/4K, but if you want to replace an aging multi-monitor setup - it's low enough to be justifiable.