Buck wrote:

The SWR on the 600 ohm line will be 600/25 = 24:1

The SWR on 50 ohm coax will be 50/25 = 2:1

For a 25 ohm single band antenna, I would be inclined to go with
the coax.

Ok, I learned something, but I would be inclined to go with the 1/2
wave of 75 ohm and then the 50 ohm

"1/2 wave of 75 ohm" would make matters worse for a 25 ohm
antenna since the SWR would be higher than for 50 ohms.
What you need is 1/4WL of 35 ohm coax like RG83.
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73, Cecil http://www.qsl.net/w5dxp