Connecting mixed-speed multiple serial devices to two microcontrollers
I would say, either:


Do this with polling, and just check the fast device 10 times as often as you check the other devices. Or..
Do everything with interrupts, but make sure they're extremely fast. Like just copy the new byte to a buffer and exit, process the data later. In this way you may be able to receive from many serial streams at the same time. This is more resource efficient, but you could create a situation where the serial coms experience occasional glitches if all devices are receiving a message at exactly the same time.