In an wireless N environment, using a salvaged N650 radio from a dead DIR-635 I was able to upgrade my Tablet PC to N. With that N card in there I was able to use a Tablet with a 900Mhz cpu and a base Intel graphics adapter to stream HD movies. When benchmarked with Chariot, I saw speeds of up to 32MBps. (300 mbps connection rate).
Now, some would say that I cheated because I used a radio from a router and not an adapter, but that just leads me to believe that the reason for poor wireless performance in N mode is a combination of Drivers, the systems running the cards and the manufacturer of the radios themselves. The technology is sound, it's just an infant. These are the growing pains of Wireless N.