with a router configured for mixed mode, are you saying that both N and G devices would be running at N speeds? i thought it would occur differently. wouldn't it be more likely that the N devices would have to run at G speed then because the G devices would not be capable of running at N speed? i could be incorrect regarding this, since I am not very fresh on my networking standards.
This is true, if you are running in mixed mode it will slow down the potential speed of the wireless N devices because it must slow down in order to talk to the wireless G clients.
Max wireless LAN speed in mixed mode will be just 54Mbps, but if you run in 802.11n Only' mode you can achieve 300Mbps. This is a significant increase in wireless LAN speeds.
The problem is that most printers I've seen can only handle wireless G which forces the network to run in the slower mixed mode. For this reason I ended up using Ethernet for my printer.