I am writing here so there is a record of this issue, I plan to share it with AMD and Acer but mostly AMD as I know they will want to do something about this.
On the Acer forums people I believe representing ACER say that the overdrive is working and is the reason the option cannot be changed on the monitors OSD. They say it's optimized, one said by AMD in the driver. I just bought myself the Acer XF270HUA which is the new version with the frameless design. The specs are 2560x1440p 144hz 4ms Freesync IPS (AHVA) panel by AU Optronics.
I tried using Freesync using Displayport on my MSI RX Vega 64 liquid and the ghosting is terrible, coming from a TN panel it's unplayable to me.
Thankfully I tried using the HDMI 2.0 port on the monitor and my RX Vega and the overdrive seems to be working on it, it's pretty close to my Benq XL2730Z which has the same specs but it's a TN 1ms panel.
It also didn't have overdrive working when I got it on displayport but I took it to Benq and they updated the firmware to version .v002 and after the update the ghosting went away and freesync and overdrive was working over displayport on the Benq XL2730Z.
I believe basically the Acer XF270HU has the same issue and has never been fixed. I am one of the lucky ones for now as it's working over HDMI 2.0 with a freesync range of 40-144hz.
HDMI isn't as stable as displayport in my opinion and I am worried about when this will stop working or if some games wont work.
One of the main reasons I am writing this is here are many people out there that purchased this monitor and don't have a HDMI 2.0 port on their GPU and are forced to use HDMI 1.4 which has a Freesync range of 40-70hz or are forced to use it with terrible ghosting.
Acer is saying overdrive is working on the XF270HU (I have the A version which is frameless) but a quick test using Fortnight and trying Display port and HDMI 2.0 and you will see that the overdrive isn't working when using display port.
I need AMD to test this and finally get around to fixing it together with ACER as it's been long enough and there are plenty of people trying to tell Acer that it's not working but with no luck and ACER saying it's working.
Another user tested it on the forum post below and said the overdrive was the same as DVI-D with overdrive off and not the normal setting ACER I believe is saying it uses.
Post on Acer community forum by user: badogblue
I have 2 of these screens side by side (1 with DisplayPort, 1 with DVI-D) and by running the following test: http://www.testufo.com/#test=ghosting it is clear that:
Overdrive via DisplayPort is identical to Overdrive disabled via DVI-D
Please explain how disabling Overdrive via DisplayPort is the same as "optimizing" it.
So I hope that Acer can finally fix this monitor's overdrive when using displayport with freesync.
amdmatt I hope you can help this issue get the attention it so deserves for all those who purchased this monitor and don't have HDMI 2.0 on their GPU. Either way it should be fixed as it's not working.