I've grown both individually in the past but as I use them for the same recipes etc I thought I'd just see how they went together in the same container. Previously I've planted all of my choy/choi seeds in their own container or spaced apart and as a result always end up with huge leaves very loosely bunched.
This time around I planted a heap of Buk Choy and Pak Choi seeds in the same container in order to keep the bunches more tightly packed and so I can 'cut and come again' with small leaves.
The Buk Choy and Pak Choi seed packets have very similar germination and maturity guidelines, however the Buk Choy seeds sprouted 5 days ahead of the Pak Choi seeds and have raced away as you can see:
In future I don't think I'll bother with Pak Choi.