I think there are considerations on where you'll be. Do you need a topo map to give your GPS coordinates? I don't think you do. You don't need a map at all if the GPS displays them. If you want to locate a safe landing zone, and you're in a city, a topo map won't help. It would out in the wood, I guess, assuming you can read it. :-> Frankly, if the rescue team has your coordinates, I'd expect them to be better prepared to locate and land at a safe place.

I have a Colorado 300 which comes with no maps, and I've loaded it with free ones that I find on the Web or that others prepare. The 400t comes with a topo map, but I don't know if it's the right area for you, nor if the scale would be useful.

I live in an urban area with lots of trail runs, bike rides, etc. for fund-raisers, and my view is skewed by the nearness of roads to the trails. I've had a chopper called once for a volunteer evacuation, but it was to land on an intersection of two paved roads near the accident. Are you seriously out in the field with no roads? I also have a Nuvi with city maps on it, and that gets me through all my 'field' operations here in this area. (The colorado 300 is for Death Valley, Burning Man, and the like.)

My thinking is I'd ask other volunteers if they use a GPS and what; get several opinions. My other thought is, I'd ask the SAR guys what they'd recommend.