> If you use a crystal, the
> freq. needs to be some binary multiple of the rate one wishes.
Not necessarily. You cen use programmable up/down counters and achieve any desired ratio. By using switches for presetting, you can get a multitude of desired speeds (as +/- 10%, +/-50%, 2X, 16X etc.). With 1024 combinations (typical) you get resolution better than 0.1%, and still enjoy stability of quartz oscillator ( < 0.01%)!
Bratislav