Exactly. Disable overscan and make frame buffer size fit to your selected resolution.
Try LE's screen calibration whenever you check a new video mode.
According to the Raspberry Pi people, overscan only affects the boot screen. Specifically NOT Kodi. I did the frame buffer size thing and recalibrate to no effect. I think it's as good as it's going to get. I just have this niggling feeling: there are pixels at the side of the screen asking to be used!! It's an analog set, so not worth buying the remote for ... on the other hand, it's got a bit of life left in it by the looks of things!
Thanks for all your input.