Yeah, I think you're right. It's a moot point anyway as despite what head office told me, when I got to the store they didn't have either on display. They only had one 50" in stock so said they couldn't really set that up for me to look at as then they'd have to sell it as open box but they had four 42" in stock, so set one of those up for me to test in the demo room.
The main thing I wanted to check was how readable the text from some PC game screenshots would be. I'd made 1080 and 720 versions of each screenshot and whilst the 1080 ones were readable for some of the games that used bigger fonts (e.g. Kingdoms of Amalur Reckoning) for others they were a bit small (e.g. Wargame Airland Battle, Men of War, DCS World: KA-50 Black Shark). With the 720 versions, naturally everything was that much larger and from about 7ft it was fairly easy to read the text in all games at 720. I decided it would be best to get the 50" though as it will make everything that much larger still and thus easier to read the text without straining and it's only an extra £100 and it seems to make sense to get as big as possible whilst I still can, considering that Plasmas aren't going to be available soon. On either the 1080 or 720 versions, I didn't notice the pixels or see anything that would concern me about gaming on the 50" at 7ft away, although as they were only static images I can't be certain that there won't be any issues with actual running games but I can't see why there should be. I played some HD clips I had as well (a couple of them (Planet Earth, Ken Ross) were ultra high bit-rate and the BD player my USB stick was plugged into struggled to even play them) and they looked amazing, regardless of the TVs actual resolution, so I've got no concerns about watching film/video content on it either.
In the main showroom with lots of TVs on display, it was surprising to me how much larger a 50" looks compared to a 42" and in fact the 42" didn't strike me as being any bigger than my 34" CRT, even though it obviously is, whilst the 50" looks much bigger (but it will be about 2ft further back than my CRT is, so that will negate some of the size increase). Once the 42" was set up in the demo room and resting on the floor, with a 55" fixed to the wall a few feet above it, strangely the size difference didn't seem so noticeable so there's obviously some optical tricks happening there but I'm quite confident that the 50" will give a more immersive, cinema-like viewing experience in my room than the 42"