I would probably hurl at that distance. Others obviously love it. It's so personal that asking for advice is actually pointless. You need to go stand/sit in front of one at your desired distance and decide for yourself. No calculator, THX recommendation, guideline or any such thing can help you make a personal decision.
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.