Hmm, do you get headaches while gaming, or on desktop usage, or both?
If the headaches come mostly while gaming, and the monitor is at a relatively close distance, then you might be experiencing the immersion effect too strongly, and you're basically getting motion sickness. Increased resolution can have slight affect on this (which in this case should thus be a reversed effect), but mostly it's the monitor size and viewing distance combination. High refresh rate can also be a factor, as your brain has a harder time interpreting whether what you're seeing is real of fake (IIRC, this was also one of the "reasonings" why 24fps should be a good option for movies - so that people would know that what they're watching is still just fiction). This is something that you can/will get used to, in time.
Also, if you have to squint to read the text, then the resolution is too high for your viewing distance. In which case you should try moving the monitor few inches back. But considering you were actually worried whether it would appear too blocky, this is most probably NOT the case.
Sometimes the PWM backlight causes headaches. But the Acer should be PWM-free (="flicker free"), so this shouldn't apply in your case. You can check this with the pencil test,
like seen here. (On the right-side laptop you can see the silhouette of the pencil, which means the display used PWM. If you can't notice the silhouette when waving the pencil in front of your own monitor, then it's PWM-free.)
If you earlier had a glossy screen, then the (semi-?) matte screen might first feel a little strange to your eyes. Shouldn't cause headaches, though, as it's apparently quite light. Actually, usually it's the other way around, meaning going from matte to glossy can cause headaches, as your eyes see more reflections than they're used to, and the brain involuntarily focuses on them all the time.
Some bias lighting behind the monitor should also help. Just make sure it doesn't shine AT your eyes, or too brightly at the wall. It should be "soft", and reflected from a surface (like the wall). Furthermore, the matte surface combined with curvedness collects light reflections in a totally different manner (in good and bad). Direct light is troublesome, but reflected light is mostly taken care off by the matte finish (from light sources behind YOU, not the monitor).
Also, be sure to calibrate the screen for a more "natural" color. Don't rely on the factory settings. You could try my
own settings for the XZ321Q (inside the spoiler) as a starting point (the OSD menu is probably identical). I use the
lagom.nl-site (gamma, black, white) as my manual calibration of choice. No colorimeter hardware needed, just your own eyes. Excess brightness can indeed have adverse effects, and even my own initial calibration was very bright, so had to tone down the white level, and readjust rest of the settings for a more correct gamma values. Occasionally the brightness still sneaks up on me. (Excess brightness causes more radical contrast differences for your eyes, and thus they have to "work harder", by fully opening and closing the iris.)
When I got my XZ321Q, it took me about a week to feel more "relaxed" to use the new monitor. Partly it was because the earlier set was 42", at a longer viewing distance, so my head movements now had a more tangible impact. As a result, I instinctively began to tense my shoulders to keep my head in place. My eyes were fine, but the tense shoulders caused headaches.
