In a pipeline ADC, you may or may not want to scale down the capacitors. You could have the same capacitor size and still could implement the RSD logic. Anyway coming to capacitor values, from whatever I have read, I would stick to 100f for better matching. Somebody who had first hand experience on pipeline adc on 0.18u could throw some light on this. Also plz let us know of what type of caps are you dealing with, whether it is metal-metal or poly-poly or any other?