[jet]

...That he would nominate Austin to gain votes. He's a smart guy, and he would know that nominating his best friend would lose him support and only make Austin fans vote even more to save him.
and why would he nom Austin, who was in the top four to be saved? It's so ridiculous his reasons have to be genuine...

If you look at what the others who nommed him said it shows how difficult Austin was being and how bad he was making people feel:

Bobby: he has an ugly side, a temper, refuses to accept people have a different opinion to him; no need for him to shout and scream and swear at people.
Natasha: he's carrying around a lot of hate and anger that explodes into the house several times a day and when he's unhappy the whole house hears about it.
Clovie: the way he addresses other HM's is unsettling, when he pops at Chloe (Stevie said) it gets his blood boiling
James: the way he treats people and goes off isn't acceptable, its hard for me because I have to make the right decision and as much as I love him how he's behaving is wrong.

James would also have known that Austin was going to get nommed and be up anyway, regardless of whether he nommed him or not.

Conclusion: James was genuine because otherwise it doesn't make any sense.