My move from a 50" to a 65" plasma led me to losing 30 pounds of weight in the plasma (and it's attached base). I'm not sure why you think the new one will be 15 pounds heavier. It might be, but my guess is that it won't. I suspect your stand will be fine, but this does not constitute professional advice.
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.