nstreme2 makes two cards to work in a different channels or even bands.
and it is normal tx rate on test to be quite different than rx rate.
futhermore, it is normal to see different values on bandwidth test in different directioons (transmit/receive/both).
Yesterday we made tests on a new cards atheros a/b/g in office.
We test four cards in nstreme2 on two stations PIII/1000MHz, ROS v2.9.46. Test gave us results 30% better than p2p link with a single card, nstreme enabled between same routers.
And on nstreme2 there was a difference on rx/tx rates. All bands 5GHz, no turbo mode enabled.