If both Tx chains are enabled, speed is low and Tx CCQ is low. No matter what of Tx chains(0 or 1) is disabled things are better. Something is messed with both Tx chains enabled. Next is Tx power, if set manual tx power and no more than 19 dbm, all is ok. Setting regularity domain and country also works good but in that case current tx power is lowered(is this true?) to 14 dbm - i can not make difference between this and 19 dbm manual. I dont have external antenna yet, will test when it is available.
With all above settings, channel width 20/40 mhz, indoors, i get Tx/Rx CCQ 99-100%, P Throughput 109226 kbps and about 10 mb/s actual download.