First off, response rates are just the time it takes for any given pixel to change colors. The only real thing lower response rates get you is smoother looking animation. Higher response rates will lead to a "ghosting" effect, where things on screen are moving faster than the display can refresh the pixels.
Now, my guess as to your problem, is that the TV is doing some kind of scaling of the image. Such as taking a 408i image and bumping it up to fill the entire screen. This requires some processing time, which you wouldn't really notice if you were passively watching TV, but doing something interactive like playing a game isn't exactly what the designers had in mind.
You can try poking around in the TV's settings, to see if there's any sort of option to turn off what I suspect is the problem. It being a Sony though doesn't exactly increase your odds much.
I have a friend that has a 40" Sony Bravia XBR and we have HALO 2 LAN parties about every weekend and there is a "lag" in the tv. Like when you press the thumb-stick to look left, there is a delay from when you press it and when it actually happens on-screen. This can make playing any first-person shooter almost imposssible. I looked at the specs for the TV and it has an 8ms response time. we were using an xbox on it now he got a 360 and we thought it mite be an input issue so we tried every input cable availible (except for s-video). Composite, Component, VGA...all of them still had the "lag". Now we are beginning to wonder if it is the tv that is causing it. ANY FEEDBACK WOULD BE NICE!!!