i am after a new tv i hae found a 46" sony tv but there is a month waiting list or i can order a 40" sony tv which i can have a day later the 46" is about £361 more the specs of the tv are both the same but the size.
£361 is a fair bit higher i suppose but whats the point in rushing it if your like me you will only curse it 3 months up the line wishing you had bought the bigger.... I Had a 50" downgraded to 42 and have to say miss it... we had a 32 sammy in the bedroom and i was toying with going for 37/40 but realistically it would be too big if its a large room id say go for the 46 if its quite not too big 40 will be more than big enough..
Get the larger size, you will only regret it afterwards. My living room is around 15'x10' and I got a 50" screen. Upgrading from a 32" CRT it looked huge at first but quickly got used to it in a couple of days. Now I am 100% glad that I went for something that size.
I sit 5' or so sometimes and TBH as long as I am using a good quality source then the experiance is even better. But then that is my preference.
As with all things related to TV's, I would 100% recommend trying it out for yourself if possible. Some people like LCD, others like plasma. Some people are OK with upscaled SD, others not so much. I got my screen set up in a certain way, other people come round and mention that theirs is set up differently. I know my dad has his setup differently.