yes, get a 50incher. i watch at 12ft and 50" now seems small. there is no such thing as too large TV(unless you physically dont have the space to put it)
it is not the question of being bad, i used to watch 29" crt from same distance
just that after a while only thing people regret is not getting the bigger screen. with many hd channels coming the issue of poor sd pq on larger screen also not a big issue.
Go for the biggest screen your pocket can afford. I also watch my 40" LED from a distance of about 11ft; I wouldnt mind a 55" or even the latest 60"cher over there... lolz..
it really depends upon your preference. I find 32" fine from this much distance. IMO, 40" will be fine, however if you want movie experience you may go for bigger one!