fed up with 2.4GHz not giving me consistent speedtest results...

tried with 5GHz with iphone 7+:
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Never heard any beeps from either my modem or router.. Both are TM supplied equipment.. Not even aware if they are supposed/capable of making audible noises..
From this features comparison page, it seems like the Asus RT-AC86U is the better choice... It has faster speeds (theoretical) on the 5Ghz band & double the available flash and RAM memory than the RT-AC87U.

Purchase wherever you feel the most comfortable.. Best prices is to buy from overseas, but you lose out warranty wise.. Because, in most cases Asus Malaysian prices can be as much as double what we can get elsewhere... Up to you to decide if warranty and peace of mind is worth the added cost of purchasing local or not..

I believe my previous response stayed which is the better buy and why... More memory tends to equal a more stable performance. Anyway, since I don't have personal experience with either.. Here..reviews..
86U and 87U
Both are respected reviewers and so reviews can be trusted. Especially Blacktubi.. He's well known for networking equipment and tests for real world usage.. Not just theoretical speeds.

AC86U currently has the fastest Asus router CPU and the newer Broadcom BCM4366E chip which fixes the 5GHz bug.  Latest batch of AC86U hardware revision is 1.5

Always buy unopened factory sealed set as you may not wish to risk picking up an exchanged unit.  No experience with overseas sets at half the price as you would not know for certain whether they are exchanged sets.  Also note there are discussions on snbforums around the Broadcom driver used in the AC86U.  Its pretty much the best router in terms of specs from Asus at the moment just some issues with the firmware which Asus will fix.  None of the issues will afffect normal usage,

You are looking at either GT-AC5300 or RT-AC86U which has the Broadcom BCM4366E wireless NIC.  AC5300 has tri bands versus AC86U which has dual bands.  Otherwise it looks about the same specs wise.

If you want serious gaming stability and prepared to get a bit technical, Mikrotik/UBNT is cheaper on a similar setup.  If you want a simplified setup and management then its any vendor gaming routers with faster CPU and gaming priority QOS.

Even 300Mbps wireless connection on 5GHz is more than enough for gaming and it does not drop on 5GHz since relatively no interference.  Of course wired is the best for gaming always.

So now you already know which to buy between the two and is quite satisfactory.. Else, you can always spring for the beasty Asus ROG Rapture GT-AC5300.... Sure zero complaints then..

Turning off Air Fairness is probably the main thing.  Game priority QOS.  WTFast turned off as gaming latency is better without it (unless for those days latency is off the charts WTFast will help).  Most of the other settings keep defaults recommended by AiProtection scan. Do not run the new router and your old Asus in AiMesh mode, its unstable.

That should get you running fast.  Other settings you can tweak once you get to understand the AC86U better.