Since the WLA2 is Broadcom-based and 11g compliant, I expected performance similar to the Belkin F5D7130. However my testing with a BuffaloTech WLI-CB-G54 CardBus card showed that Buffalo's "throughput hopping" behavior is still present as shown in Figure 2.
Figure 2: Four location throughput
Further testing with a Belkin F5D7010 CardBus card - also 11g spec-compliant and WPA-enabled - showed that the "hopping" seems to be related to the client card and not the WLA2. A close-range Condition 1 test with the Belkin card showed a steady throughput plot - although not without a few significant throughput "dropouts" - with average throughput of 22.6Mbps compared to the 20.8Mbps average obtained using the Buffalo Tech card.
This doesn't necessarily mean that the Belkin card was better. I ended up comparing Condition 1 throughput in three security modes - WEP 128, WPA-PSK / TKIP, and WPA-PSK / AES - for both cards and found odd behavior in each case. I was especially concerned at the drastic difference between two runs taken a few hours apart for both cards.