Im running the same Adapter and rev2 version, and im getting around the 200 mbps Mark with excellent (5ghz) and like 3 bars with 2.4ghz. My router is in the basement and my adapter is on the 2nd floor. The signal has to travel through almost 4 feet of flooring as well.
I find that changing the channels can increase the signal. I use channel 11 combined with using 802.11N ONLY.
Try setting your channel width to Auto 20/40. That allows speeds to be boosted up beyond 130mbps but it is very unstable for me. However since you are getting about 6 mbps it should hopefully push it past the 54mbps mark.