Hi Michel,
Are the bit clocks going to be synchronized? or you are going to sample each stream bit separately based on its clock? I think the LPC43xx family of high performance MCUs could achieve the sample frequency you need:
LPC4300 Series: High Performance Microcontrollers (MCUs) based on ARM® Cortex®-M4/M0 Cores|NXP
Please notice that processing an interrupt takes time, it takes you 12 cycles to get into the ISR so whatever the GPIO pad is physically able to do, the determining factor is the time you spend on going into the ISR and run the ISR.
Hope it helps!
Best Regards,
Carlos Mendoza
Technical Support Engineer