65" will look great in my opinion.
I think the 55" uses IPS screen (Better off axis viewing but you sacrifice blacks) and the 65" uses VA Panel. So make sure the off angle viewing is not a deal breaker for you. I however think the 65" is the way to go, bigger is better
If I am wrong on the panels someone will chime in but I think I am correct.
Current Sets: Sony XBR75X940C, Samsung UN48JS8500
Previous Sets: Sony XBR65X930D, XBR65X900B, XBR49X830C, Samsung JS9000, JU7090, JU6500, JU6400, HU9000, HU7250, PN64F8500, Vizio P65, LG 65EF9500, LG 55EC9300