What is the tradeoff running the DDS input clock beyond its max input clock rate specified in the data sheet?
Typically, exceeding the maximum clock rate of a DDS device increases the power dissipation, which raises the die temperature. This temperature rise can be calculated by the following formula:
TDIE = TAMBIENT + PWR(Theta JA)
You should not exceed the maximum junction temperature specificed in the data sheet. Overclocking may also result in spectral degradation due to the violation of internal timing requirements (internal setup and hold times), which are thermally sensitive. If you exceed the maximum specified clock frequency of a DDS part, you do so at your own risk.