andylb said:

The maximum supported memory speed is 2400MHz. The RAM speed that is above 2666MHz is only achievable with overclocking. In other words the 3200MHz you want to purchase is overclocked RAM and the overclock is applied through an XMP(extreme memory profile). The MOB does support 3200 but the Acer BIOS doesn't support the overclocking(XMP) needed to run it at 3200 and it can't be unlocked.
If you put a 3200MHz memory in your system it will work at 2133 or 2400MHz in other words the frequency supported without overclock.

Please click YES if I have answered your question, thankyou

JordanB said:

@accers

It appears the GX-281 has an auto XMP feature.....that I wasn't aware of.  Thanks for pointing that out.
Clearly it gives it a boost in performance based on the userbenchmark.

Unfortunately, I don't know the max speed.  I don't know if you should buy the Crucial XMP 2666 or XMP-3000 or the XMP-3200.
This "auto XMP"  feature isn't officially supported by Acer that I'm aware of.

There's nothing you need to do in the BIOS.  It should all happen automatically.   But I don't know if the BIOS has it capped at 2666 or 3000 or 3200 or some other number.
Only one way to find out.

Compatible ram is in link below.

https://www.crucial.com/usa/en/compatible-upgrade-for/Acer/aspire-gx-281#MEMORYFilters

Edit:  The part in your userbenchmark link is below.....a pretty impressive part.

https://www.crucial.com/usa/en/bls8g4d26bfsek

Edit2: Just to let you know that the Crucial Sport LT won't work properly if you mix it with your existing ram.  It will run at the same speed as your Acer OEM ram ----2400....or possibly even slower (and make you disappointed).  So please don't mix it with your existing Acer OEM ram.

It looks like a normal overclock I don't think there is a XMP and those guys probably unlocked the bios because they cpu frequencies different tho.I ask to Crucial by the way they sad '' yea it's %100 compatible but you should be able to configure memory specs''(even 3200mhz) and ''Ok, because even for 3200 mhz memory, you might need to configure its XMP in BIOS settings''  ''However, my suggestion would be to access BIOS because you will need to update the bios version to the latest'' 

I send mail to acer for ask them too new bios for gx 281 because i sad them '' all b350 motherboard support second and third generation Ryzens and 3200mhz it need just 5 mb BIOS JUST 5 MB '' but they didn't do that.It simple you ask American Megatrends for new bios and they release it.It's simple because of just 5 MB why i need to sell my motherboard my windows key my Memorys what the heck is that.I can't understand. I regret to buy Acer product i have no idea they always say'' your motherboard support 2400 mhz and 1700x 2400mhz 1700x 2400 1700x'' like a robot.As I said how difficult it can be It just 5 MB BIOS .Whatever i just regret to buy acer (there is nearly %30 performance difference between 2400mhz and 3200mhz there is a nearly %80-100 performance difference between ryzen 1600 with ryzen 3600 but we can't use that because of the 5 MB BIOS) ok whatever.