Thanks for the data, very illuminating. The numbers here are half the flow figures given by ORR, presumably your table is one way whereas ORR's are both ways?
Interesting how high St Pancras is, and combining that with Kings Cross sheds a different light on ORR's table of top 10 flows with one end outside London, showing Cambridge actually has similar flows to/from London as Manchester Piccadilly and Milton Keynes.
For local commuting into Cambridge, Royston is number 2 behind Ely, though there are significant numbers of long distance commuters into Cambridge from London too.
One thing I've learned from your table is that Whittlesford and Audley End are a long way down.
When I go from Cambridge to London I've started to use St Pancras more than Kings Cross. While it may tale a little longer you can always guarantee a seat. The non-stoppers to KX are always packed.