The only people that can tell you how big a TV should be for you... are you (and people you live with).
For me, an 80 would be gigantically, massively too large at 10 feet. Even a 70 would be too big at that distance, albeit just slightly. For Suzook, the 80 would be fine at 10 feet.
Is he wrong? No. Am I? Also no.
The only answer for you is your answer.
There is no difference in HDMI cables. If you can see the picture without visible dropouts or sparklies, the cable is working at 100%. No other cable will display a better version of that picture. You're simply wrong if you think there is a better digital cable than one that is already working.