I'm not sure I should post this as I suspect it will cause you to go into full meltdown

Without attempting to go technical 1080p isn't as good as the mfrs make out, it can be a lot better at the right viewing distance with the right content but it can also be worse than 720p. At 4m with a 40" TV i'm fairly sure that all the extra detail will just blend in and look no better than 720p. What you have to be aware of is that non-HD content could suffer bad pixelation because the sky box has to upscale it fit your screen (try to imagine it doesn't have enough pixels to fit your screen so it expands the picture and trys to 'guess' the colour in between pixels).
The other consideration is Plasma VS LCD. The difference is getting less now but a 1024*768 plasma can give give a better picture than 1920*1080 LCD depending on what you display through it.
Simple comparison:
LCDs now rarely suffer screen burn (if a static picture is displayed for hours), plasmas still carry a risk of this (Panasonic have fairly much beaten this on their plasmas)
LCDs are better for PC inputs.
1080p LCD will display blu-ray DVD's better
Plasmas display moving pictures better with less pixelation (footie, grand prix etc)
Plasmas tend to have darker blacks (contrast)
Plasmas tend to handle bad signals better due to the lower resolution and way they work(freeview, non-HD sky etc)
Your best bet is to read avforums.com but trust me those guys are ott about everything so you need to read between the lines a bit

And just so you know after 3 months of convincing myself I needed a 1080p LCD I ended up buying a TX-P42C10 1024*768 plasma and i'm very pleased with it
