Thanks Chad
The room is not that big, the AP is 2 metres away from the laptop and on the same level. I get full bars up in the menu bar, I am currently sat downstairs with the same reception strength (full bars). The 3/4 - 2/3rds refers to the signal strength indicator in the internet connect window, which is a solid bar.
I know it is practically impossible to achieve full 54mbs, having read a review where they were only getting 22mbs from the same AP, and considering that to be good, I guess 3/4 of total signal strength is not too bad. Would be nice to be able to measure it though.