Maximum wifi speed with OpenWRT? (802.11a Turbo mode aka Super A)

 
Hi, we have been testing what is the absolute maximum speed over wifi when using openwrt, for out test we used this hardware:
 

• 2 x Ubiquity Router station
• 2 x Wistron CM9 802.11a/b/g mini pci cards
• 2 x 3dBi omni antennas
   
• openwrt version - backfire 10.03.1
• wifi driver - madwifi
• distance - 2 meters (same room)
• encryption - psk2
   
  For benchmarking we installed iperf package and used default settings (tcp packets in one direction).
   
  First we tested "plain" 802.11a mode (hwmode 11a) on channel 40 and we got 30-35Mbit speeds.
   
  Then we switched to 801.11a turbo (hwmode 11ast) and got 55-60 Mbit speeds.
   
  Is this the maximum speed possible? Are there any other tweaks we can do to get faster speeds?
   
  Did you get faster speeds? How? Which gear did you use? We didn't make results artificially better by using udp packags, my guess by using udp packages we could get near 100 Mbit speeds.
   
  Are there any openwrt tutorials for tweaking and benchmarking maximum speed?