After several configuration glitches, some Windows 7 upgrade issues and changing equipment etc. I finally achieved a stable residential wireless network. What is unique to the setup is a repeatable condition the cause of which is beyond my technical ability to understand. The network speed is 12 mpbs most of the time. At some infrequent point during the day or night the speed drops to 8 mbps. This is not a gradual drop but a step function down to 8 mbps with no change made to anything connected to the network. Since the drop really doesn't change the network functioning significantly to be visible at the time it happens, I have yet to capture the moment it happens.

If I release and renew the IP addresses using the router web page access the speed returns to 12 mbps and stays there until the drop occurs again. This is a repeatable phenomenon which works every time it is done and I have been using it for two weeks to maintain the 12 mbps when I discover that the drop has occurred.

Equipment is as follows running using standard setups.
Motorola SB6120 Docsis 3.0 Cable modem connected to Charter ISP
Dell windows 7 using a wusb600n v2 adapter
Dell Windows Xp using a wusb600n v1 adapter
HP Pavilion DV6000 lap top with internal wireless n compatible adapter
Xbox game with a WGA600n adapter
WRT600N Linksys Router

I would be much obliged if someone could explain why this drop takes place and especially why the drop is reversed by a release/renew of the IP addresses at the router.
Mike in TN