This may be of use:
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The exact example parts picked are just ones I have in my collection; the Q factor is a property of the core material. (The MS part is a Sendust mu=60 type.)
Once you know Q factor, and core size and shape, you can estimate its power dissipation rating (say using a typical watts/surface area figure) and therefore its VA. In a typical 10% ripple DC converter application, you get as many VAs from the DC W output.
So, a core that dissipates 1W and has a Q of 100 can handle 100VA. A converter operating at 10% ripple can deliver 1000W DC.
Or in a resonant converter, you may need comparable or greater amounts of reactive power, in which case you need the Q that much higher, for the same watts output.
Tim