Ok, This is strange...
The Airport card in the MBP connects to my wifi router and shows in the Network Utility a link speed of 144Mbit/s.
But under Boot Camp and Vista the link speed shows as 270Mbit/s.
Each of those numbers could be transitory and temporary, shifting from moment to moment as they renegotiate.
If those numbers are consistently the same after many re-checks, it could be choices made in the drivers. I think the driver software might be in control of the tradeoffs the wireless card makes with relation to speed versus link-stability.