I've honestly never noticed any real difference in my internal network (though I only stream lower grade video I usually just run HD stuff locally from the machine in the main room, and since my internet rarely sustains a speed above 2 MB/s It doesn't really come up there. I would say on average the n is about 100kbs faster than the g in that scenario. ...that could just be signal strength though.
In my experience where wireless really fails is with downloads where a lot of connections are in play, like with a torrent or p2p download scenario. I've had results from both N and G that include, loss of connection, loss of connection data resulting in no connection, significant choking when many connections are active at once regardless of signal strength, high number of failed hashes, and other such annoyances when using wireless for p2p. Though it does not seem to suffer the same problems in a usenet scenario or normal download/stream where there is only one to four or so sources.