That sounds like a nice start! I'm not sure, though, if that number includes retransmissions and/or unacknowledged frames. IIRC i think i've seen that TX number grow in an interface with such a lossy link that was just sending traffic (trying to reach the distant ap) but getting nothing in return (ap couldn't hear me)
So far, with openwrt and ath9k / ath9k_htc, i've found the "tx bitrate" (or MCS level) a fair indicator of the link capacity. if it says "65.0 MBit/s MCS 7" i cannot tell exactly how much goodput it will have, but i can be pretty confident that it will be better than when it says "6.5 MBit/s MCS 1"
Good point on ifconfigs potential limitations.
One issue with using the wireless sync rate is that fresnel zone infractions will allow you to sync at one rate but for the link to fall apart as the throughput grows. I have seen a 130Mb link degrade to 54Mb as soon as it started passing significant traffic.