largest tv that 720p will look good on

[lazydays]

I view my tv from about 10-12 ft, most of my content is 720p (or lower), and I'm wondering what size tv I could upgrade to without making everything look terrible. I would not consider myself to be picky about video quality but I don't want it to be irritating either. Given this criteria what size tv do you think I could move up to?

ps I'm currently using a 42" plasma tv and I'm very happy with how my video's look on it now. I don't see very much in the way of artifacts or blocky dark areas. They may be there but I don't notice them.