Hi,
My PC clients with .11N adapters say they are connected at 300 Mbps....but the router Wireless Connections Page reports 54 or 48 Mbps speed(s).... So who knows... At least now, for me, the router is showing the .11N clients instead of showing them as .11G clients.
I can also point out that one of my .11N clients, a trendNet wireless gaming adapter, was showing router speeds of 104 or 108, but listed it as a .11G device. Now showing as a .11N device, it reports speeds at 54 Mbps.....
Also it seems the encryption cipher has some impact of speeds, but I can't say that for sure....more o***ut feeling. I am no cipher specialist but I suspect the math used in the cipher process is different between TKIP and AES....thereby resulting in slightly different wireless performance....

?
SD1