I think Gus wins rather easily similar to the Shogun fight. As long as he doesn't get KO'd which I guess is always possible with Machida. His size will give Machida problems.
Machida was the first person to get past the reach of Jon Jones which is longer than Gus' and rocked him and he's the only person whose ever KO'ed Rashad Evans. He's also not a sloppy brawler like Shogun is, Machida actually throws stuff besides wild haymakers.