I am trying to understand how to estimate the frequency capability of
a voltage BalUn made by winding two insulated wires, in bifilar
fashion, around a ferrite core.

For instance, I have made one, with two 23 turn windings, that
exhibits a paralleled winding inductance (at 253 kHz) of about 568
uHy. The two windings in series aiding, exhibit (at 119 kHz) 2550
uHy. The two winding in series bucking, exhibit (at 5.7 MHz) and
inductance of 1.15 uHy. And the capacitance between the windings is
about 154 pF. The total wire length in each winding is about 1.2 m.

Neglecting for now, the high frequency roll off of the ferrite
material (which is similar to type 43), is there a way to estimate
over what frequency range this voltage Balun will act as a fairly
ideal transformer, based on these measurements?

Thank you for your assistance.