(yes, we're reading the topic, but there's not much info about this, I'm afraid) (personally, I've only used my lovely NEX-5N, and yes, it overheats like crazy)
I have been using NEX 6 for some 5 months now and so far absolutely no overheating problems whatsoever. Most of my clips are pretty short, so 5 would probably be fine, but I wanted the viewfinder.