I can't point you to any study or data, but I've worked around WiFi enough to know that beamforming is one of the first optimizations performed in multi antenna scenarios, mainly because of how easy it is to do. A 3dB bump in SNR for a 2x1 antenna configuration might allow you to transmit at the next modulation depth (QAM16 vs QPSK for instance). That will increase throughput and reduce the retry rate. At low SNRs it can increase router range.