Hi Ian,
I have used the red and white mix from
www.cwsbytemark.comThey are low perm materials and as Frank said, stable with flux and temperature. 25w should be easy to do. Lean towards the RF parts with small Ur because maybe the power supply types of stuff may wander too much. I used a stack of 2 T130-15 parts for 300uh at 8 amp for my modulator. If you are using a multi pole chebyshev or similar then you know that the inductance will probably have to be more accurate. Frank and Todd helped me out with suggestion of a series trap on the modulator output which really clobberd the switching noise.
One way to test inductor is to place a steady voltage across part and watch current rise. Rise should look like straight line all the way until it curves up when it actually saturates. Other way which may be even better is to run a dc current into the inductor and have a tertiary winding that you can measure the inductance with a small ac signal - In effect generating your own Hanna curves.
73
Bob