Quadrature decoder capability of Rabbit RIO

Hi all,

I would like to use the peripheral chip Rabbit RIO to read the quadrature signal from a motor. In the datasheet I find the max. frequency of 40MHz for the RIO chip. What is the maximum count rate of the quadrature signal that can be measured at 40MHz RIO Clock?
Is the quadrature encoder input independent from the Clock Input (Pin CLK)?
Is the SPI Clock independent from the Clock Input?