I find phones around 5.5 to be ok, and have no problems pocketing or handling them. But that really is the largest I'd want to go myself.
I actually saw a OnePlus One, the first time in the wild today. Although the person using it was apparently a phone dealer, handing out these flyers in the street outside of a middle school.
Oppo has more than 20 different phones in their current range for the domestic market, including a few that will only really fully work with China Mobile. And only about 2 or 3 that properly have the US bands in them, no CDMA. And to actually buy one, the official distributors for North America, Oppo Style are in Hong Kong.