Max 802.11n rate betwen two rb751u-2HnD

RouterOS Wireless Networking
1

First rb751u-2HnD is AP
Second rb751u-2HnD is station
802.11n
Indoor
Bandwidth on station test show send and receive rate about 160 Mbit

If station is asus usb-n13 or tp-link tl-wn812n I get send and receive rate about 200 Mbit

Why the rate between the two routers is less than the rate between the router and the usb WiFi?
What is the maximum rate between the two rb751u-2HnD?

2

Try to low the tx power.

Sometimes with N and too much power, the datarates are low.

3

Low speed (160) due to the high CPU usage (95%).