Definitely 27 inches or more - 32 if you can afford it.
My 27-inch ViewSonic has 2 inputs, DVI and VGA. Recently the DVI input failed, so I have to use the VGA via a converter dongle. I really don't see any difference. So I would say go for size and high resolution, regardless of the input format.
get a real big one.
Better two.
This foto shows 2x27" aside:
and:
my recommendation for you: 2x65"
yes. you are reading it right.
check out samsung_uhd_tv. 65"
with your i5/GTX970 you can raise resolution to max even on a large tv.
forget about the times we differentiated between PC-Monitor respectively TV, they merged.
See how it was tested on foto (4 days ago) below:
hope that helps.
If you want it really big and real, get the Oculus Rift 
Lol, that is so true. I have a 40 inch 4K monitor but when I want to really fly my sim. it's always with theOculus Rift, you cannot beat it for the immersion, it's just like real life flying.
i think he asked for monitor.
32" 4k monitor works fine on a nvidia 960. If you think of a 4k tv check out this site http://www.rtings.com/tv/reviews/best/by-usage/pc-monitor
Oculus is where to go for simming!
But if you need a monitor, I highly recommend a Dell ultra-widescreen. I have the U3415 and love it -- fills the whole field of view.
I have the LG 34UM58-P and have been very happy with it. It is hard to beat the wide aspect ratio, IMHO.
https://www.amazon.com/lg-34um58-p/s?ie=UTF8&page=1&rh=i%3Aaps%2Ck%3Alg%2034um58-p
I know I know.. question was about monitor.
however without any pressure < GET OCULUS RIFT > sorry I've must get carried away 
No seriously, your system is perfectly capable of running Aerofly in VR.
That is way more immersive, than even ten 80" monitors in spherical setup, trust me..
For flight sims, Oculus definitely has the edge for immersion, it just becomes a totally different experience to a desktop/monitor setup. However, if you also use your PC for other stuff, then a monitor is much more versatile. Half the time I still use my monitor for flying and driving as the level of detail you get is way ahead of the rift, and sometimes you just want to get in and go without strapping the thing on. Dual monitors work very well for flight sims, as there is often a frame line down the centre of the cockpit, but do you ever play a driving sim? if so, the bezel being right on the vanishing point is a bit irritating, so triples are better if you have the PC power.
I've been really happy with my 34" ultrawide. For me it has been the best all round solution to flying, driving, shooting stuff and, er, actual working on the PC. Triples are bulky and support is not always that good in games, but the single monitor doesn't have to worry about this. Also, as a monitor rather than a TV, you can have it really close on your desk, so the angle of view is not that far from using triples anyway. You tend to have triple just that bit further from your eyes.
I actually use the 34" ultrawide as my main monitor, and have an old 19" LCD next to it, so in X-Plane 11 for instance, you can have all the detail on the main screen and a live map browser on the smaller one.
