First off, "high-speed" mode won't really give you anything. It only helps if you're flying stick-banging 3-D aerobatics in a high-performance helicopter. Otherwise, any effects will not likely be noticed at all. This has been confirmed by people who are world-class aerobatic flyers. For airplane flyers, there's no advantage to using it.

For your setup, you can use S-Bus or not. If you put the aileron servos on four adjacent channels, you'll get the speed and precision you'll need. In 2.4 GHz operation, if the four aileron servos are on channels 1-6 or 7-12, they'll be in the same grouping.