RT-AC66U (378.55 Merlin) with Macbook Air (2013) 5ghz wifi speed

Hi,

I'm trying to find out, what my max. wireless speed is with my Macbook Air (2013) combined with my RT-AC66U.

I use the 5Ghz band and my internet connection is 200 / 20 Mbit/s (down/up)

When I do a speedtest with cable I reach the 200 Mbit, but when I use my wireless connection I get 140/150 max.

Is this the limit or should I get higher wireless speeds?