More preliminary results:
Fancy beamforming stuff and 1000 mW maximum output power in Apple's Airport Extreme 802.11ac does not seem to measurably improve maximum range vs. their Airport Express 802.11n with lower maximum power. That makes me sad.
On the other hand, inside that range, something in there is clearly improving my connection speed. I get a full 300 Mbit/sec for a fair distance from the device, and a generally higher transmit rate across the whole functioning region. Since my Macbook doesn't even support 802.11ac, my guess is this is some combination of better antennas (there must be some reason that thing is so gigantic), higher transmit power, and beamforming features. (In retrospect I guess it makes sense to me that beamforming can't help much at long distances. But it saddens me anyway.)
So far both Airports have noticeably longer range than other APs I've tested. But there are several more to go.