Hi
SiLabs datasheets are so and so when it comes to clarity. The current datasheet says that Si5351A can go up to 200 MHz. However, the max VCO frequency is 900 MHz, and with the then "forced" divider ratio of 4 this results in a max output frequency of 225 MHz. Is this within or outside of the spec? Not really sure - one could argue that the 4 divider cannot work properly above 200 MHz, but it does. However, many VCOs can go close to 1200 MHz from where the 300 MHz comes from, i.e. 1200 MHz / 4, but, again way out of spec., and not all Si5351A will be able to do this. My experience is that a "guaranteed" fmax is 280 MHz.
Bottom line: 300 MHz is a lucky punch, i.e. may work and it may not. I would not put any money on it.
Bo
Bo, OZ2M