I have $400 for an upgrade, what to do?

I have two PC's and know one needs an upgrade more than the other, but I also am happy to know that if I upgrade my one PC, the other will get some decent hand-me down parts. Here are the specs of the two PC's

http://pcpartpicker.com/p/32SQn - The Stronger PC


http://pcpartpicker.com/p/32T0j - Not as strong, but has been a great PC


Don't judge me on either PC's parts, I did what I could with the money I had on the first one, and the second one I got the whole thing when all those parts were fairly new (before the gtx 7xx series and before Haswell) and got them for less than $400.

Now that I've said that, my nicer PC I have an ACER h236hl bid IPS monitor that I love, but on the other computer I have a monitor that basically my friend gave to me, but I don't intend on keeping it, I want to give it back, also, it's TN and I love IPS so I would like to upgrade with that, and if i was to upgrade, i'd probably get a 27" 1080p IPS monitor because i think 1080p looks fine on a 27", and I know I couldn't handle 1440p. I would obviously take the 23" to my other computer, and give my friend his monitor back. The other option is, I get a gtx 760, and give the 7870 to my other PC. I have $400, and am looking for recommendations, feel free to recommend things other than what i've said, and feel free to recommend I simply save up for something. Thanks in advance to anyone that helps. :)

Depends on what you want to do on each computer.

You can make the weaker computer have greater performance with a GTX 760 or R9 270(X).  Upgrade the RAM to 8 gigs and it's a nice budget rig.

Or you can get a nice IPS monitor.  You could probably afford a 1440p korean monitor, but you'll need to get a more powerful/more VRAM graphics solution.