I'm not sure but I assume the signal range is determined by the rounter antenna and the positioning of the unit. Obstacles such as walls/doors etc also affect the signal/range of the device.
The speed however is determined by the cards/adaptors. to get 108Mbps, you will need all the cards to be of the same speed.
I have a netgear 108mbps router, but my laptop is centrino and only works at 54mbps, so I'me getting that speed.