I've been looking into possible locations for this Mustang task and come up with a few ideas. We see the driver wearing a helmet, implying that this is not taking place on public roads. So the private location needs to have the wide expanse where we see the white Mustang performing donuts on, and also a long straight with forest cover that we see the red Mustang speeding through.
I'm fairly certain Taiwan doesn't have a facility that fits this description, let alone even a single race circuit. We also know of quite a large number tasks, more than the average first leg, so I will be very surprised if it is Taiwan.
Looking at Indonesia, I can't find any information on any circuit other than the Sentul Circuit posted earlier. Watching a lap of this circuit, its clear that the footage doesn't fit here. Ford don't have a production plant in Indonesia, so the Mustangs would have had to have been shipped over, unless they were hired from a third party.
Looking over the circuits in Thailand, a possible fit is the Kaeng Krachan track. If you go to 1:30 on this video, the trees on the right seem like a possible match. http://www.youtube.com/watch?v=lHCOpLxugCQ
However, the lighting of the Mustang shot implies that there is tree cover on both sides of the track.
A notable feature of the red Mustang shot is the long grass. It is unusual to see such unkempt greenery in a top-class circuit, unless it was a huge facility. This made me look into Ford Testing Facilities. We saw teams take a ride on the Mercedes-Benz test track in Germany in Season 9, so why not again with Ford? Ford have no testing grounds in Asia, but apart from one in the UK, the only other one in Europe is in BELGIUM: The Lommel Proving Ground.
The facility itself is huge, with a large variety of tracks which are all closed to the public. As a result, there are very few videos of the track itself. Of the few there are though, they show evidence of narrow straights, undulating terrain, forest cover on both sides with very similar trees to the ones we see in the footage. In short, some parts of the Ford facility seem to be a perfect fit for the Mustang task.
We've wondered why there was virtually no sightings of the race in Belgium. The test track is quite removed from any major city, so if teams were touring the remote Belgian countryside (or maybe even the Dutch as well; the border is only a couple of miles away) for this leg, no wonder we had no info.
Still no concrete proof, but at the moment, this is my best guess..