There are a number of conflicting recommendations for optimal viewing distance, which I speculate is because of different personal preferences (e.g., see where people take seats in a theater where there are lots of empty seats), the nature of the material being viewed, eyesight.
My best recommendation is to pace off the viewing distance at home, and then go to a brick-and-mortar retailer and pace off that distance from some potential screens to see how you like viewing from that distance, hopefully with something representative of what you would be watching on the screen.
Looking at "Optimum HDTV viewing distance
" Wikipedia page (yes, Wikipedia doesn't have that good of a reputation here on AVSFORUM, but I am using it to show a sample of the breadth of recommendations), one comes up with a variety of recommendations for 10-ft viewing distance
|Diagonal Measurement||Recommending Party|
|48"||viewing distance = 2.5 x diagonal (20 degree viewing angle)|
|75"||viewing distance = 1.6 x diagonal (30 degree viewing angle) SMPTE|
|100"||viewing distance = 1.2 x diagonal (40 degree viewing angle) THX|
My main TV viewing distance is about 1.7 x diagonal size, and my bedroom TV viewing is about 2.2 x diagonal size (the larger distance/diagonal ratio or smaller viewing angle is an advantage for reducing the annoyance of compression artifacts on cable and for viewing shakycam like Blair Witch Project or Cloverfield, but a disadvantage when viewing fine detail or letterboxed content, and the smaller screen is good when tuning to one of Comcast's music channels to fall asleep to by reducing the amount of light in the room).
With the wide range of recommendations, you can see why I recommend going to a store and viewing a variety of sizes playing material typical of what you would be viewing at your home viewing distance.
Of course, screen size is but a single dimension and has to be tempered with other factors, like picture quality, budget, and what ports you need your TV to have.
I'll add just one additional note: with the exception of being too big to physically fit in its target location, I don't think I have ever heard anyone regret buying a TV that was too large