...25 watts to an omni? 50 watts to a vertical?

I have hit the ISS with 500 mW to an Eggbeater.

But, G1OCN is right. When the ISS APRS transponder is on, there is ALWAYS traffic. It receives very well, and transmits a very decent amount of power.

Jeff, when you say "vertical"...just what type of antenna are we talking about?

John KB2HSH