Generate high precision frame

Hello to the community

I need help please for a new project to find a NI card

I need to generate frames with a period of 600us ± 1us (ie 1666.67Hz ± 2.7Hz)

I was thinking about a PCIe-6323

Problem is: counter accuracy is 50ppm of Base clock (100kHz) = 5Hz

Same for all the others boards I find, accuracy is 50ppm of a 100kHz Base clock...

Would you have any idea of material for this application ?

Cédric