I view a 57" at 8.5' and see no pixels until I get within inches on my HD Content and often I see none on quality material. My only regret is not going to the 65" when I could've had it for a mere $1500 more at the time. My TV never seems to small and is great being as large as it is for everything I view but still I crave the 65-70" at the same distance. Your Dad is carrying CRT SD 480i Concepts forward into the age of HD where even mundane viewing of local news in HD can be amazing - there are no negatives going larger unless you fail to feed it HD.
People settling for a 37" - 40" at that distance still have CRT SD on the brain which is nonsense. I had a 45" previous in the same spot and I've had zero desire to view it in my alternate room since having the bigger HT size panel. Once you go big you never go back as more WoW Factor comes with the package that's even better than a Movie House experience and I'm not exaggerating.
Same two million pixels get larger and bring out more details with dot mode 1:1 (Just or Pure et al) and the thought they don't hold clarity at larger size is utter nonsense that goes back to 4:3 CRT 480i dinosaur CRT's - do not judge a wide screen HD 1080P panel like you do those CRT's - I had a 36" Sony CRT that was great but my LCD blows it away with HT immersion - the CRT was to be watched
while these panels are to be EXPERIENCED
I cannot think of one single negative with my larger panel outside the price I paid for it nearly 2 years ago and the thought of what's lost in a 40" at ten feet is ludicrous - go view the THX VD Calculator and you'll see a 40" is a weenie size certainly not HT size at 10'.