It's not much of a slogan, but yes. I think you should stick with that. "$1m guaranteed, payed out in bitcoins"
We must do better than that, don't you agree? How about 1,668 BTC currently ($1,000,000) GTD. The irony is that this works out better for us anyway as we were calling it the 1,500 BTC ($1,000,000) GTD but now we can be more precise by adding currently.