Switchmode transformer wire winding size

[rtarbell]

When winding toroid transformers (standard 50/60Hz frequency), I have heard that a good rule of thumb to use for wire thickness is 700 - 1000 circular mils for every amp of current that runs through the secondary (and likewise with the primary).

==> Is this rule of thumb any different when winding switchmode transformers? I know that the transformer core itself, along with filter caps, can be made smaller when operated at higher frequencies, but what about the wire size of the transformer windings?