I didn't know that radios have an SWR warning. I will have to look and see if that's in my manual. I Probably wont run that radio at 75w until I get a real base antenna and or a much better mag-tenna. Until then I think I will be just fine at 25w which is the next highest setting. I was able to get out and rcv great on 5w so I will probably leave it there until I need to bump it up. If the worst thing it will do is ruin the antenna and not the radio maybe I will check it out when I have another antenna for back up.
One of my first contacts on VHF was at 5 watts into a homemade j-pole about 5' above the roof into a repeater about 100 mi away. You can do a lot with 5 watts if the terrain is right.