the way i see it is, the difference between thx calibration or any other calibration from avforums or avforums settings and professional calibration is going to be what 10% at best imo. nothing like the "quite big" you claim it will be.
£300 to get a marginally better picture is a waste of money imo. especially if you take into account it is 1/3 of the price of a brand new 50" GT50 (£899).
a bit like buying a £21K car then spending £7K on it to get 10% more performance, even though it is likely to be less than this number.
i think you are expecting it to be a HUGE difference, but the difference is going to be minimal.
look at the avforums review
http://www.avforums.com/reviews/Pan...ch-Full-HD-3D-Plasma-TV_287/Test_Results.html
Pros
Excellent black Levels
Impressive contrast ratio and dynamic range
Lack of PWM noise and clean looking images
Very good out-of-the-box colour gamut
Reference colour gamut after calibration
Excellent out-of-the-box greyscale
Reference greyscale after calibration
Reference level 3D performance
As you see it gets Excellent scores out of the box with no calibration what so ever.
Therefore with settings from AVforums should mean your basically at reference but not 100% the way there.
Your going to end up paying £300 and having practically the exact same picture. In fact I would be surprised if anybody could tell the difference from settings on avforums and a professionally calibrated screen when it comes to this specific tv, because it is so good out of the box.