that have nothing to do with BFS or not, it's simply the work frequency of in/output tasks. So, the time accuracy of a synthesiser, for example, depends on this setting. BFS or not.
Realtime in the kernel tree didn't mean "as fast as possible", it mean accuracy, a exact time schedule table, reproducible at any time, under any circumstances, stable in latency. Otherwise you get jitter, like you describe in your statements above.
greets
brummer