It would seems I was mistaken; I thought my TV was 42 inches but on measuring the screen, I'm getting about 1.2 metres on the diagonal (that's how TV size is measured, right?) which google tells me is around 47 inches.
Still in "720p worth it" territory according to the chart though, which lines up with my experience as far as different resolutions go. Anything 720p or above looks good on it, provided that the content itself is visually attractive.