[Amps] confused reading amidon ferrite specs?

[Dan Sawyer]

I have to say I am very confused reading Amidon ferrite core specs.

http://www.amidoncorp.com/aai_ferritecores.htm

As an example in the paragraph description material 61 and 67 cores are 
good for transformers up to 200 MHz while in the spec sheet the 
transformer claim is 500 MHz and 1000 MHz respectively.

I am interested in building a solid state 1200 watt power amp for 160 
through 6 meters. What are the materials suitable for the input and 
output transformers in that range?

Thanks - Dan - kb0qil