Hello every beta tester, current openwrt(or lede) default wifi driver is not very well.
My test result of iperf is around 12Mbps.

Thanks to nobblepepper test result:

1. With the image(mtk driver) that came on VoCore2 I get:
$ iperf -c 192.168.1.1 -t 30 -f m
--snip--
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-30.0 sec   191 MBytes  53.4 Mbits/sec
$ iperf -c 192.168.1.1 -t 30 -f m
--snip--
[  3] local 192.168.1.177 port 39644 connected with 192.168.1.1 port
5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-30.0 sec   212 MBytes  59.3 Mbits/sec

2. With lede with mt76 driver I get:
$ iperf -c 192.168.1.1 -t 30 -f m
--snip--
[  3] local 192.168.1.177 port 39712 connected with 192.168.1.1 port
5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-30.0 sec  44.5 MBytes  12.4 Mbits/sec
$ iperf -c 192.168.1.1 -t 30 -f m
--snip--
[  3] local 192.168.1.177 port 39713 connected with 192.168.1.1 port
5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-30.0 sec  38.4 MBytes  10.7 Mbits/sec

3. When I disable cal_free data like this (which gave me BIG
improvements in speed on MiWiFi and Linkit7688)
https://github.com/openwrt/mt76/issues/28

I get:
$ iperf -c 192.168.1.1 -t 30 -f m
--snip--
[  3] local 192.168.1.177 port 39775 connected with 192.168.1.1 port
5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-30.7 sec  7.75 MBytes  2.12 Mbits/sec
$ iperf -c 192.168.1.1 -t 30 -f m
--snip--
[  3] local 192.168.1.177 port 39776 connected with 192.168.1.1 port
5001
[ ID] Interval       Transfer     Bandwidth
[  3]  0.0-30.5 sec  7.00 MBytes  1.92 Mbits/sec

Here is a firmware from mtk openwrt, wifi works very well.
http://vonger.cn/upload/openwrt-mt7628.sd.bin
default password is 12345678

This firmware is only for one antenna. I disabled another one.
It is easy to enable by update factory setting section. update 0x0034 of factory setting to 0x3422(old should be 0x3411)