This will depend fully on the codec in use. Modern video compression can squeeze quite a bit of data over USB 2.0s speed(480 megabit = 60 megabytes, but in practice, you get more like 30-40megabytes/second.).
I would give it a try, I remember recoding FRAPS to a USB drive at those kind of screen resolutions.
I can also watch bluray without even the slightest issues over USB 2.0(it is in a USB 3.0 case, but connected to 2.0). It is good for 6-8x read/write speeds(27-36 megabytes/sec)
I would say to give it a shot. Worst case, you need something faster. Best case, you have what you need already and did not buy something for nothing.
Keep the drive defragged(any hard drive for video recording should be kept clean with a minimum of fragmentation) to avoid frame drops as well.