ac AP, mixed n/ac clients - any drawback?

i have an ac AP that is now serving 2 clients. priority is high speed to the 1st client, and decent speed to the 2nd client. this was mounted around 2 years ago.
ap is a dyna, the clients are ~800m and 1km away in the same direction (around 3 degrees apart from each other).

one client is a disc ac, other client is sxt ac. the client with sxt is getting bad signal because a tree grew up and is dropping modulation and i was thinking to replace it with lhg 5 or lhg 5 xl (non-ac).

can i replace the sxt with a lhg or lhg xl (AN, not AC)? i’m using 80mhz channel.
can 1 client use 80mhz, and the other client use 40mhz?

my reasoning is that it’s better to have a good signal on AN modulation (so it can stay all the time max on 300mbit), than to have an ac client with bad signal that often drops to 87mbits.


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