Aah - so the DOF on 4:3 is more to do with the physical kit you have available, rather than the aspect ratio? I misunderstood there!
Recording time is only limited by the card and batteries really, although at 1080p I think the longest clip you can film is about 8 minutes (max file size output).
Here's a couple of vids done with the 'filming' in mind (rather than just gathering clips of riding, if you get me):
And a 'pretty much completely dark' test: