Well, I have one AC link using NV2 and got 140Mbps throughput with 1 TCP connection.... no problem to achieve over 100Mbps on speedtest.net.. But its just one NV2 link behing fiber and 24GHz radio.
Ok you are right, I have just switched one link in between NV2 (3 in row) where I was getting only about 10Mbps with single TCP connection from NV2 to Nstreme (single chain 40MHz N) with the settings described here:
http://forum.mikrotik.com/viewtopic.php?f=7&t=83183
And now getting nearly 50Mbps with single TCP connection.. so it really seems 3 links in chain running NV2 cause low single TCP throughput (even with 10 TCP connection I was not able to achive same throughput like I do after switching to nstreme).
Try the setting described in the thread above, it seems it help in some cases.. for example just one link in the middle of 2 NV2 links..