The question is, is there a way to come up w/ a rough estimate of the mix
value? I wound some test coils and come up w/ these figures:

T-50 15turns 30awg = ~150uH
T-37 9turns 30awg = ~180uH

Perhaps there is a chart or something similar somewhere that I have
overlooked that will give me an idea.

The equation goes;

Turns = 100SQR(uH/Al) where Al is the inductance in uH per 100 turns)

and

15 = 100SQR(150/Al)

and (0.15)^2 = 150/Al

and

150/0.0225 = Al = 6666.

You have ferrite not powdered iron.

For Ferrite, it's just the conversion

Turns = 1000SQR (mH/Al) where Al = mH/1000 turns

15 = 1000SQR(.15/Al)

and
0.15/0.00225 =66 which looks like, (for T50 core) material 61

W4ZCB