Larger or smaller is dependent on format size. What is good for 810 is going to be way large for 120.
Both extremes will give a softer image for different reasons, too scientific for the likes of me. I think there's a calculator on f295 also.
If you like the 210 FL that's the FL you need to do the calculations for. Keep in mind, it will be optimal for 210mm not 150. It will be usable but the
exposure will change because the relation between the FL and f stop has changed ie: f250 is no longer 250.