So about 6 months ago I got an Acer XF270HU, which is a 1440p 144Hz IPS Freesync capable monitor, and about a month ago I got a Freesync capable GPU (RX 480). Over the past few days I have been doing some testing and here is what I have found. I didn't start out this post meaning to write a full on monitor review, but what the heck. This thing was not cheap so I would never want to give people too little info.
First off, sadly this monitor does not have a VGA port, only Display Port, HDMI 2.0, and DVI-D. I have tested a cheap Porta VGA to HDMI adapter based on the MS9282 ADC, and it does work fairly well with some caveats, which I will mention below.
First off and probably most importantly, 400 line DOS VGA modes do not display at all sadly. I am not 100% sure if this is due to the VGA to HDMI converter, but I am fairly sure it is the monitor itself. If anyone knows of a graphics card that can output such graphics modes over DVI let me know, I would love to test that. I also have an external scaler (Crestron HD Scaler) that plan on testing, but I have not gotten around to it. EDIT: I should mention that many VESA modes do work, 320x240, 400x300, 512x384, and up do work. It seems that 200/400 line modes are just the exception.
Now, for old computers that output a 15khz signal all is not lost, if, you have a line doubler. I have a MiST FPGA which can run as many of the classic 8 and 16 bit computers outputting either the original 15Khz video signal or a simple line doubled 31khz signal. For the most part this monitor has had no major problems with the line doubled 31khz signal, 15khz is a no go though. I have tested it with the C64, Amiga, Atari 8-bit, Atari ST, ZX-Spectrum, Amstrad CPC, and Apple II and it syncs just fine. Both 50hz and 60hz work just fine and the scrolling is perfectly smooth with no inserted or dropped frames. The only issue I have is the pixel clock is not correctly identified on some of the cores, mainly the C64, Amiga, and Speccy, so there is some vertical banding. Not a big deal to me, but it may bother others more. Also had some problems with getting the ST to run at 1280x1024, but that could be the MiST implementation or my drivers.
Finally we come to DOSbox. Before I got a Freesync capable graphics card I tried setting up several different display modes to get smooth scrolling. I just never could, no matter what I set it to, 60hz, 70Hz, 12hz, 140hz, 144Hz, things still stuttered. Games I typically test for this Tyrian, Commander Keen 4, Epic Pinball, and Pinball Dreams. 144hz definitely helped, but there were still obvious hitches. Now that I have a Freesync capable card, it's perfect. I didn't have to setup any custom graphics mode or anything, everything just syncs and scrolls smoothly now. No screen tearing or stutter in any of the games I have tested. It also seems to work just fine with the output set to whatever (surface, overlay, DDraw, D3D, Opengl, Openglnb). I did the most testing with the GOG version of Pinball Dreams since I am very familiar with that game. Outside of having to set my fullscreen resolution in the .conf file it pretty much worked great out of the box, where as this game in DOSbox without Freesync just made me want to toss things across the room. Pure joy now.
For modern gaming it has been a great monitor, but I would not say life changing over the typical 1080p/60hz monitor. I personally am not one of these people who can see a huge difference between 60 fps and 144fps. The only game I have noticed even the slightest difference in was Battlefield: Bad Company 2. I could tell a small difference when it would drop below 75 fps. Again, small, slight, probably wouldn't have noticed it if I was not sitting there trying to see it. Hell, without the FPS counter I may not even noticed. There needs to be a good scientific ABX test for this. Basically I would not recommend this monitor for it's high refresh rates outside of it's Freesync capabilities. Freesync has made a noticeable difference to me in gaming. I also do not claim that it is the panacea that many claim for low frame rates. No, it does not make sub-30 fps smooth or anything like that. What I have found it does do is when you are above 40fps, things do tend to seem smooth and there is no noticeable frame judder for ever changing frame rates.
I also would recommend this monitor who enjoys vertical shmups as it is rotatable and looks fantastic vertically due to being IPS. Having tried several TN monitors for this before I can definitely say the difference is night and day. Many of the choice shmups available on Steam look and play great on this monitor. Mame games are also excellent due to the Freesync. No special config necessary, don't even have to turn Vsync on, everything still syncs perfectly and smoothly.
I apologize if all this is a bit long winded and off topic, but again, for something so expensive I certainly want to give all the facts I can. If there is something in particular you would like me to test with this monitor, please let me know. If I am able I would be more than happy to do so.